Here are a few points that you need to keep in mind
- Have a positive mindset
- Try to replicate the same problem in another site
- deactivating and re-activating all plugins and themes
Steps to troubleshoot the problem
- Backup (Real time backups if possible, database backup, regular backups)
- staging site
- conflicts tests (check the compatibility of different plugins and themes with one another and with WordPress)
- wp health check plugin
