Mailbox stuck between A53 & R50

Brief system description: We use the ZCU106 evaluation kit and the included ZU7EV device is equipped with a quad-core Arm® Cortex®-A53 application processor (the A53 is running in a Linux environment), an ARM Cortex R50 processor is runs in the FreeRTOS environment and an ARM Cortex R51 bare metal processor.

We are having a major problem dealing with 2 mailboxes, A53 R50 and A53 R51:

The system speed is 148.5 MHz
FIFO size:
Mailbox_1 8196
Mailbox_0 16
The threshold for MAILBOX R50 RIT is 4096x32bit = 16Kbytes.

The problem is that after a certain period (variable time) we have an indication that the FIFO on the R50 side is full and R50 cannot write new data - this means that A53 did not read new data from the FIFO buffer in time. Register Mailbox Status Send Status = 11 - FIFO Full.

It should be noted that A53 works at the same time (in parallel) with 2 mailboxes with both R51 and R50 and there are also additional processes in A53.

Any idea why after a certain time it is stuck? Is anyone else experiencing the same issue??

This sounds like a problem with the receiver, running Linux.
Make sure that the receiving processes on the A53 are created as round-robin, real-time priority tasks, each having the same static priority. If there are other high-priority real-time processes on the A53, they may be starving the mailbox tasks.
The Linux scheduler executes the highest-priority, ready-to-run real-time process. The process runs until either it is blocked by an I/O request, it is preempted by a higher priority process, or it calls sched_yield(2).
Round-robin processes also run for a time slice if sharing priority with other round-robin processes.

If the processes are not real-time, then the Linux scheduler may preempt them to run lower-priority processes, resulting in non-determinism.

You can also try to slow down the sender for confirming.