I think that the odds of the problem being an actual firmware bug are pretty mych zero, given that the OP was associating the traffic he is looking for with the wrong service type, appears to be confused regarding the difference between frequencies and talkgroups, and went from using GPS to provide scanner location to a ZIP code, which is far less accurate. As to the "wild and crazy" ideas, they are exactly that. If encryption was being used, there would be some indication that was the case--either ENC showing on the display or garbled audio. The remainder aren't worth contemplating. If a firmware bug disabled 800MHz frequencies, there would be hundreds or thousands of affected users (including me), and there would be a huge thread about it already.
What is far more likely that system changes were made in the main database, such as updating site location info, the service type tags on various talkgroups, etc. and those changes were written to the scanner during the same write to scanner as the firmware update.
Also, turn on all Service Types, make sure there are no Avoids set on the systems or departments within the systems, and that all quick keys associated with favorite lists and affected systems are still active. Reconnect the GPS so the scanner thinks it is where it actually is. Temporarily increasing Range is a useful diagnostic, but will cause the scanner to scan a lot of out-of-range clutter.