There is known issue with this chip. Siemens fixed it in version 5.3.
In certain conditions the issue which you described is happening.
Check voltage on KNX as above 30V this was happening. The biggest issues were with combination of SE KNX PSU.
Check if you don't have some script which is creating a knx loop
Check if some device on KNX network is not spamming the bus.
If nothing help we could replace this chip on your LM. I assume your device is out of warranty already as it is old one.
Yes.
1) Bus voltage KNX 23.2V (PSU Mean well dr-24-30 together with PSU for knx bus EVIKA (CHOKE-KNX)).
2) Errors "Transmitter Error(send 0 receive 1)" occur in other LM's in the serviced building.
also seen the same at customer SL, now with 1.5.1 fw, not to old - ap 2 years... But not take attention to it - all functions are working fine..
But what does mean ''too many devices''??
I had other problem - very long KNX lines.. Not possible to divide it... I just added second KNX Power Supply to one line end, and first one reinstalled to other line end and finally all works. Not a very good solution but possible and solved problem..