Retrieving Data from records becomes slow intermittently

We have a solution based on record centric approach, hence all the database tables are mapped to Records, which have relationships too that vary from 3-4 per record to 10-11 on some of the records. All the interfaces are using records to display the data, recently an issue has been occurring while retrieving the data from records has become dead slow, causing time-out errors, or sometimes the interface takes forever to load. I have looked into the performance logs and server logs for any related cause and made certain performance improvement changes too but the issue still persists. The issue occurs intermittently, hence it is hard to figure out the exact cause of the issue. I'm looking out for what could be causing this and the best solution for this problem.

Thanks in advance, your help is highly appreciated.