Extension registration timers

My clients has a combo of LinkUs extensions and IP Phones. My IP phones runs on an LTE APN built into the unit. When my client dials from LinkUs to his IP Phone, the call would cancel at random. No ring or indication. On the logs it says "No Answer". Sometimes calls go through, other times it doesn't. I'm suspecting there is an issue with the registration timer. What would be the most ideal timers for a cloud hosted Yeastar with remote LinkUs and IP extensions?