Have you tried different bridge services to see if it's the bridge?
Look for some free conferencing bridges so you can test without cost.
It might just be the service you're using.
It could also be associated with your outside line provider.
If you have T1's, check them by entering the command:
list measurements ds1 log xxxxx
where xxxxx is the T1 board location. If you see error seconds on the board, you might want to look into the configuration of the circuit, or the health of the DS1 board.
Carpe dialem! (Seize the line!)