There are (sadly) a multitude of potential problems involved in this thread.
First, to the person who has battery drain: it's not the zwift companion app, per se, that is draining your battery. It's that your set up is somehow necessitating your phone's connection tech (bluetooth radio; wifi receiver) to do a lot. And it may be something you can't fix (e.g., IOS is notorious for having bluetooth and/or wifi drain batteries).
Bblair, I had the same issues, and worked with the same presumptions for solutions. I will add a note of editorial vitriol: I think Zwift is just terribly-executed software (albeit some great game design). Buggy, old, and they have a super-messed-up (please use profanity here, even though I can't) tendency to blame USERS (!!!!!) for not having Apple TV or their preferred configuration.
They're a dreadful software company behind an absorbing and fun cycling game. Reduce your expectations accordingly.
Ultimately, I had to consider the following variants:
- Zwift not only was frequently updating (Nov, 2020) but the updates were addressing bugs and were themselves buggy. You really might want to uninstall and reinstall the master app.
- You have a dual-band router. I'm already into a long post, so I'll try to keep this overly short: use 2.4Ghz networks for whatever is running Zwift AND Zwift Companion.
- 2.4 can compete with bluetooth. What a headache, but I solved it thusly: I just turn off my phone's BLE before I go near my garage.
- Yes, I tried ANT+ and for the sake of brevity will just say that my laptop / KICKR CORE / Samsung phone trinity seemed 'happier' when the phone had its bluetooth off, the laptop only had to talk to the CORE (and a HR monitor).
- Boot sequence mattered as I was sorting this out. I'd reboot the KICKR, boot the laptop, then start ZC on my phone.
My final observation could well be hallucination: for some reason, after I metaphorically banged all of these teensy details around, I had several stable Zwift sessions in a row. I hadn't done anything differently, and this was NOT across a Zwift update. Nonetheless, it seemed almost that the devices "got used to" looking for one another, and now even though nothing has changed the entire set up is far more stable. In fact, it's up and running within 60 seconds.
I wish I knew enough about such tech to tell you why that may or may not be a real observation, but I can tell you that as an end user, I find it exasperating. Zwift's Eric Min sure has made the rounds on media about how he raised $400M in VC and is going to take on Peloton with a smart bike, but he can't drop a few mil to have a less-finicky product? THEIR SOLE PRODUCT, I might add, unless you consider the posters and jerseys part of their path to world domination (hint: it isn't, it's just clever marketing).
As a final (probably tiresome) remark on this topic, I am also a Rouvy rider and find that Rouvy unintentionally makes my point about how shoddy Zwift is as a programming house: Rouvy has horrendous on-boarding, profoundly sorrowful websites, and has committed so many GUI sins (THREE separate applications??!??!) that it is remarkable they are still in business. They are hapless.
However, once you start pedaling, their software .... just works. And works well. I had literally zero issues with connecting to Rouvy and making it work. In fact, despite finding much about Rouvy to be Keystone Kops level tragi-comic (one example: multi-ride "challenges" that tell you how many - but not which rides - you've completed), it has a great feel to rides, and of course: routes from around the globe.
If the hamster-on-treadmill, stoned-German-grad-student outfit that is Rouvy can connect to my stuff, what on earth is Zwift's excuse? (BTW: one of their buggy 'updates' not only wasn't addressed for six days "because it was a long holiday weekend" (LOLOLOLOL ... million users get effed, eh?), they simply stopped responding to support requests during that time. You'd have been forgiven for thinking they'd gone bankrupt. But hey, no, they just had a bad week, I guess. Which wasn't much comfort to people who saw 30 miles worth of training rides freeze and crash.
I digress.
Try the tweaks I listed to make your set up work a few times in a row, and maybe you'll get the same stability I did. Or not. Zwift only knows.