E&M on E1 is relatively not standard and the PBX may differ from the router in running the protocol.
If you cannot absolutely configure PRI for this connection, thing that would solve the problem, please send here relevant config, and output of "debug vpm signal" for one successful and one unsuccessful call.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...