First I'll say it is entirely possible that you have a max of 220 (mine is 211) and that there is nothing wrong with that.
The caveat - this is often the figure that you'll see if you pass an electric fence or under a power line - so you may want to do a test under controlled conditions to really measure your max and then calculate your zones. If you suddenly see your hr jump high rather than raising steadily suspect some outside influence.

Another thought - you say you spent 50 min in zone 4/5 - was that calculated from a max of 220 or 197? if it was calculated from lower number and your max is actually the higher one you actually spent your time in zone 3 (as calculated from a max of 220) rather than zone 4 (in any case there is nothing wrong with spending that much time in zone 4/5 - it won't hurt you)

As far as power and hr being linked - No! that is one reason that people prefer to train with power. When you look at power numbers it is much easier to see if you are tiring or overtraining. When you can no longer maintain your target power its time to slow down - but with HR you can still theoretically push your hr high even as your power output drops, so its easier to over do it.