As @GreenFlux correctly advised to you, before/after expression is not gonna work in showif constrain.
[_THISROW_BEFORE].[Column Name])<>([_THISROW_AFTER].[Column Name] , which is basic expression and usage of before/after as trigger condition, which would work in workflow setting, but it is not working in other place such as RESET ON EDIT or somewhere other. In those place where the expression does not do the job, remove [_thisrow_after]. operator, then it becomes workable.
Obviously this is a bug, I have pointed out to Appsheet dev team sometime before, but obviously the problem still persists.