Fatal DB query syntax error on rules search - Civi 5.0.0 and recent Civirules
I do not know without checking on your site. I have recently tested 2.1 on an existing site and it worked there. You might want to check if the civirule_condition table is still populated? It might be that it got accidently cleaned out.

If that is the case, you will have to take note of what your conditions/actions where, run the sql scripts insertCiviRulesConditions and insertCiviRuleActions from the sql folder of the extension to re-create them. And then you have to rebuild your rules in the UI.