Midair interference hits
Lynx is correct. If a crystal breaks it no longer works. But if it partially fractures it will become intermittent. This happens more often than you would think. I've had two (2) new crystals do this in the last two years.
Check and clean all your receiver plug-in connections. Check and clean your switch with contact cleaner. Load-test your battery.
...But don't write-off your crystal as being good. A swap would be prudent at the very least.