while working with salesforce flows, you can get following error/warning message and its not allows you to activate flow. but it don't show which element actually have this issue. so we have to check all elements.
Salesforce Flow Error on Custom filter condition
Invalid condition logic: Your filter must use parentheses around successive AND and OR expressions.
It is because of non proper filter logic with your flow. I mean, AND and OR conditions are not handled properly. let me show you the some sample filters.
here we have to update the filter condition, OR condition should have closed braces like below.
(1 OR 2) AND 3