Recent HR issues on Forerunner 235

I got a Forerunner 235 last summer and it was working pretty much perfectly up until a couple weeks ago. I took a couple weeks off of running because of a minor injury, and ever since I started running again I've found my heart rate to be much higher than before, despite the runs being just as easy if not easier.
What I've noticed is that the heart rate measured by the watch shoots up almost immediately after I start a run. For example, on my run yesterday, the heart rate went from about 80 to 150 within the first 20 seconds of the run. Sometimes, even before I start my run my watch will randomly tell me I have a heart rate of 130 despite me not moving, and just by feeling my heartbeat I can tell it's very off.
I know the wrist heart rate monitor isn't reliable, but it was working perfectly before so I don't see why it shouldn't work now. I'm kinda bummed out because it's caused my VO2 max to drop down from 67 to 63...
Anyone else experiencing this issue or know what might be causing it or how to fix it?