I also experienced the crack of back cover.
First the transparent one (made in 2016) which cracked endlessly . I changed it to a black one which I nad ordered in 2016 … which started dismantling itself . the two materials of which it is made seem to expand with time or temperature (it is about 30 degrees here, impossible to bond them back together .
Any advice ? I do not feel investing some 40 euros again in this phone ( changed the broken screen - took 9 months to get- , the battery ( still poor autonomy ) and the camera module … I am afraid I will have to buy another brand ( for 100+ euros I can get now one with the same performances than FP2, isnt’ it ?). Any advice , idea to get a back cover at reasonable price ?