On the balance of probability the tamper fault lies outside not inside the control panel.
Intermittent tamper faults are notoriously difficult to find so you will no doubt need the services of a good troubleshooting engineer before you lose your sanity !
For information a tamper fault could be related to.....
Control panel cover
Remote keypad cover
Bell box tamper return voltage low or missing
Cover on a detector
Faulty cable
Alarm Engineer Bristol, July 2008