I too had the same cycle with a swappa purchased apple watch 4. I then followed some earlier advice I saw here and the phones I had on 12.xx and 13.xx said I needed to upgrade the phone first. I couldn't uninstall the watch app either as my primary apple watch was still paired, this was for family sharing account for the 7yo. I reset the series 4 40mm 2 times, there was conflicting advice here, I held the crown and button until the apple logo, I tried the crown till apple then the button till reset but gave up on the button, let go and reset it again. Definitely a break that needs a fix from apple. Good luck!