If you've updated OTA it's probably a good idea to flash the handset with the UK/Global firmware, it might also be worth flashing the emmc as well, though if you have anything stored on the phone make sure you back it all up to a pc or the other n900 before flashing the emmc.

The reason I say this is that OTA updated have always been shockingly bad and more often than not did more harm than good.

Flash the phone, see if it corrects the issue.