Kentico 12 Custom table data multiple choice values not visible in the grid

Are there any errors in the Event log? Have you tried re-signing macros? Are you using latest hotfix? I just tried it on 12.0.103 and it is working fine.

Currently working with v12.0.101. Tried re-signing the macros but it took a long time and it just timed out. Is there a way to just sing the macros for custom tables ?

I would rather recommend temporarily extending the time out settings in the web.config file as well as on the SQL server side. Or, you can use the RefreshSecurityParameters method. You will need either the data set or data class info object to resign macros just for given object type.
Are you able to reproduce the issue also on a newly created custom table just for testing? Or, on any other K12 instance?

I extended the time in the web.config and db and it still timed out because the db is too large, breaks on some customtable that hat 3M rows of data. I made a new custom table but the issue still persits. Haven't used RefreshSecurityParameters method. Do I need to make a custom class/hander to use this method just to update the macros for custom tables or is there any other alternatives ? Regards

You can create a custom class or e.g. a scheduled task with the mentioned method and then execute that task so its code will be executed.