Something wrong with a custom module

Hi there!

I hope somebody can help me with this problem.

For some reason one of my custom modules (Module_A) behaves weirdly on both SuiteCRM 7 and 8.

On S7 I noticed that on the relationship fields of Module_A on any related module (Module_A One-To-Many Module_B or Module_C) the auto-complete feature doesn’t work at all, I always have to use the pop-up window to choose my record.

I could live with this, as it’s not a huge deal, but the real problem starts after successfully upgrading to SuiteCRM 8.

On S8 Module_A is empty in list view, but every record is still in the database, they are available from reports or history.

What could be the problem with this one custom module?
Every other custom module with the same relationships work normally, only this one works weirdly.

Thank you for your help!