Hello Julius,
regarding your post about RX diversity and rx path imbalance,well i had a lots of those,my most hated alarm:) and it was always a different problem.For example(my experience):
RX diversity lost- could be CXU(most of time),booster(TMA),or Current injectors(if TMA),incorrect RX Diversity mode defined in the BSC or rbs sw itself.
RX path imbalance- jumpers between antenna and booster,water in jumper connector and antenna,even a loose antenna due to heavy winds