SLC5/05 data link timeout alarms

When communicating between SLC5/05 and a third party, we are receiving sporadic timeout alarms...by sporadic, I mean it could be hours to days apart.
The program scan time is very short…only 20 msec maximum & 10 msec average.
Do you have any suggestions for resolving this issue?

Also, is there a way to determine communication rate or communication scan time?

Thanks!