I've posted this issue I've had a few times already, but it bears telling again.
MICS 5.0 running PRI clean for 3 years. Cut over to new service provider, and started dropping calls. CO tested clean with tberd on site, and verified config correct.
I upgraded to 6.1MR. Same issue. The KSU was accumulating RAI's, and resetting the card every 10 min., or so, dropping the calls.
As a last resort, I upgraded to 7.1, not expecting any change. Everything started running clean, and has been working fine ever since.
Old provider- 5E switch, New provider- Siemens switch.