Upgrade 7.10.29 to 7.13.4 recommended?

I’m currently running a customized CRM system using SuiteCRM 7.10.29. The system works fine for me but the server OS and everything hasn’t been upgraded for a while.

I hired an agency to upgrade the whole system (Ubuntu, SuiteCRM) and the backup routine. They upgraded to 7.13.4 for the moment.
Now I have lots of bugs due to the customization of the CRM and not that much time for bugfixing.

The old system works really fine for me. I’m the only user of the system.
It only runs on a hosted server because I work remotely.
Would it be an option to keep 7.10 or maybe just upgrade to the latest 7.10 release?
What are the potential risks?
Thanks in advance!

I can understand that’s an issue with customized modules.

You need to update code as per PHP 7.4 requirement for it. Also, provide me agency contact who upgrade your system. I may need in the future.