If you encounter problems, you should set up the debugging flag, usually debug=2 should be enough. The messages are divided into Asterisk and mISDN parts. mISDN Debug messages begin with an 'I', Asterisk messages begin with an '', the rest is clear I think.*
Please take a trace of the problem and open a report in the Asterisk issue tracker at https://issues.asterisk.org in the "channel drivers" project, "chan_misdn" category. Read the bug guidelines to make sure you provide all the information needed.