I have had the secondhand Lumia 925 since march it came with black upgrade on it, in april I tried the developer preview of 8.1 and the phone kept locking up randomly several times a day so I went back to wp8 and it was absolutely faultless, the other day it upgraded to cyan and once again started to lock up a few times a day, on the glance screen the clock just freezes and the only way to use the phone is to do a soft reset. Any ideas would be welcome. Cheers K