Apple Watch Series 4 shutdown

My Apple Watch series 4 shuts down after an hour or so of wear. The only way to get it to restart is to put it back in its cradle. It then magically comes back on and the battery is also fine as it registers a significant % of life. I tried unpairing it and setting it up as a new watch but the problem persists. It suspiciously dates to exactly when the 5.3 update occurred although I can't be 100% certain. There appears to be no way for us mere mortals to "reinstall" watchOS 5.3 so I can't try that. I noticed someone had a similar issue with a series 2 in these forums but the advice given was to set it up again and re-pair it with the iPhone and nothing more to that thread so I have exhausted the options I know of to try. Thanks in advance.