This will be more information than you asked for but most new owners benefit from the following information gained from a lot of collective experience with the Clarity.
As you indicated the one thing people really loved about the Volt was that it could drive all electric all the time. I can understand that, if you have 50 miles of range and are driving only 30 miles today then there seems to be no reason why ICE should come on even for one second. But with Clarity it sometimes does. The way I look at it, the car saves me tons on gas, even if in that 30 mile drive ICE pops on for a few minutes (which it normally doesn't), that is a tiny amount of gas used. People who do most of their driving within EV range report going months without even having to look at the fuel gauge, any inadvertent occasional ICE usage is tiny in comparison.
Okay but still why does ICE come on, just to annoy us? Well of course there are reasons even if we don't agree with them:
1. Honda decided that some people might not find that the maximum acceleration of the electric motor powered by battery alone is powerful enough to move the 4,000 lb car to their liking, so Honda decided that when you request/demand high acceleration then ICE will come on to provide additional power. This makes sense but has some drawbacks. First of all there are people like me who find the battery acceleration perfectly adequate. Not great but adequate. I have driven other cars with not so great acceleration (like my original Prius) and I didn't consider it unsafe, I just knew to avoid situations where my well-being requires scooting out quickly in front of other cars. Other people probably feel it is unsafe to be underpowered, so I understand Honda's decision. But too bad they didn't give us a choice, like maybe in Econ mode ICE never comes on, but in Normal or Sport it does. Everyone would understand that if you think the acceleration is too wimpy in Econ then you use Normal or Sport and ICE will kick in for the extra power that people crave. But they didn't give us a choice, they just went the safe route and have ICE come on when you floor it no matter what mode you are in.
1B. You can usually avoid ICE activation by keeping an eye on the blue circle during hard acceleration and try and keep it in the blue, in my experience this will almost always keep ICE from coming on. But in hard acceleration situations I am normally not looking at the gauges so it is very easy to accidentally blip it past the blue for a fraction of a second, which then activates ICE. And once ICE is started it stays on until it reaches full operating temperature (apparently an EPA requirement). So that half-second accidental blip of the accelerator pedal causes ICE to run for several minutes. Not a total waste as it generates electricity during that time, but still a little annoying when you didn't mean to do it.
In Sport mode it's really easy to accidentally activate ICE, in Normal mode I rarely activate ICE. In Econ mode you really have to make an effort to activate ICE, as the detent, which is the click that you feel when you press the pedal all the way, is used in Econ mode to mark the point where ICE will come on. So if you drive in Econ mode and train yourself to not press the pedal past the click, you can usually keep ICE from coming on. As for me, I drive in Normal mode and accept that sometimes I accidentally activate ICE. But for me it's pretty rare.
2. Using regen with a full battery will activate ICE. This especially happens to people who charge to full, then have a downhill slope just after leaving their house. Part of this is understood, if the battery is full then there is no place for regen to send the electricity so it has to use the friction brakes. In addition to this most hybrids will have the motor spin the cold engine to use up the electricity coming from regen. However Clarity for some reason starts up ICE in this situation. There are guesses and theories why it does this but we really just don't know why. And once started it goes through its few minutes of warmup. To avoid this you can either not charge to full, which some people think is better for the battery anyway, or if charged to full then drive more cautiously during the first mile or so and try and avoid too much regen. Some people find that in winter they can avoid ICE coming on by turning on the heater to full which uses up some battery power before they reach the downhill. But that could lead to the next issue:
3. In cold weather, even though Clarity has a resistive heater to provide cabin heat when the engine is not running, if it's cold enough outside and you have the heater on, if it thinks the resistive heater isn't supplying all the heat needed then ICE comes on. This is not documented well but it's something people have reported.
4. If ICE has not run for a long time (we think maybe two weeks or so) then it will come on just to lubricate things. This is known as system check. But while system check is often blamed for ICE activation, I think for most people it will rarely if ever do system check because most people use ICE at least once or twice a week.
Okay as for the app. Different people can have problems with different parts of the app. But not everyone has problems. As for me using my Samsung Galaxy 9 the app works really great, I use it literally every day to schedule my charge times because I have a time of use rate plan where I get a low rate during certain nighttime hours. And each morning I turn on the app to see what the battery level is after last nights charge session. And I often turn on remote climate about ten minutes prior to going out to my car on hot or cold days. In eight months of ownership there have probably been five days when it didn't work. And three of those days were in June when it worked for no one from Friday through Sunday one weekend, we think the problem was on the Honda server and it was bad timing that it went down on a Friday, as the Honda app people were probably gone for the weekend by the time complaints started coming in. Monday morning they had it fixed. There was another situation about a month later when it was down for a day. Other than that, for me it's perfect. Now it does require that the car is in cell phone coverage, in my garage it apparently gets good cellular connection because it always works when the car is in my garage. There have been times however when I was parked in a multi-level parking garage for example and I could not use remote climate because the car was not getting a cellular connection (it uses AT&T network from what I have been told). I'm sure the same could also be true if I was in a remote area outside of cellular range.
I realize that doesn't help you if the app isn't working for you, I'm just saying the app itself works but for some unknown reason there are people that have problems with it on their particular phone. Many of them are helped by contacting Honda tech support, others who try that only find it a frustrating waste of time and the problem still occurs. But you might try calling them just to see if it's something they can fix. Sometimes we think it's the user account that gets messed up, as Honda tech support will ask for the account ID and password so that they can try and duplicate the problem on their end, and they often are able to fix it. Although it can be disconcerting giving out your password to someone. Maybe change your password to something temporary before calling them, then after they are done fixing the problem (or not) then you can change back to your original password.
