Sorry I can’t tell for your second issue.
Maybe the bug can come from a change in a configuration file (Nginx, PHP, etc)…
First time it happened, I did a fresh install of WordPress (for now i’m running a VPS test, this is not my prod website). Next time, I created a backup of YunoHost settings and WordPress app. I restored this backup when I got again the 502 error. I don’t know if its the WordPress restore or the settings restore that fixed the issue.