
Contact between the module and the case exists by means of a spring loaded piece of metal on the module and a pointed metal piece in the case. Sometimes, there is not adequate contact between those two pieces of metal.
I remove the module from the watch and bend the metal contact on the module out slightly to increase the spring tension between the two contacts. I then take a q-tip and clean both surfaces with rubbing alcohol. Most of the time that will resolve the problem. I ran into one situation where there was dried up glue covering most of the pointed contact in the case. In this situation, I scraped away the excess glue, cleaned with alcohol and then reassembled the watch.