Sorry to hear about your observation tray. It could also be condensation building up? You could try some diatomaceous earth which could help absorb moisture and also act as a bug trap. You can then empty it easily when it’s full of bugs or moisture.
Did you paint your roof with a couple of coats of waterproof paint or sealer? p.15 of the manual: https://www.honeyflow.com/media/docs/Flow_Hive_2_Assembly_AU_2018.pdf