Some sync problems are not constant, with the connection coming up and down repeatedly at seemingly random intervals.
Check for environmental causes
A DSL bridge is a delicate piece of electronic equipment. RF or EM interference from outside of it can disrupt its ability to function. Lamps, speakers, and dimmer switches have caused many intermittent-sync problems that are easily solved by moving either the bridge or the interfering device further away. Malfunctioning streetlights and cordless telephones can also cause problems, as can other electrical devices that emit EM or RF signals strongly. Situating your bridge near a Jacob's Ladder or Van deGraff Electrostatic Generator is an excellent way to damage it.
Check your wiring:
Make sure that your DSL bridge is plugged firmly into a non-filtered phone jack. If the wire appears to be damaged, replace it with a normal telephone cord.