I've had 4 pixel watches now. The first 3 were the first gen and every one of them did this. They replaced the first 2 under warranty before the 3rd one ran out of the warranty. The 4th one is the current Gen watch. I really didn't want to buy another one given how the first Gen went, but they are the only ones with the hourly activity reminders that actually make sense (imo) out of everyone (other than apple, but I have an android so I'm not paying for a watch I basically can't use).
If your watch is still in (or even close) to the warranty, they were pretty good about replacing it.