I upgraded the firmware on the A2 controller mounted on a S 900 platform but now its not connecting to the HiTec optima 9 receiver with D-Buss anymore. I tried downgrading the firmware to A2 assistant 1.2, 1.4, 1.6 and 1.8 but the problem persists. Any leads?

Does you Assistant show a little padlock on it? Or a video of your assistant would help....

Yes it does show a padlock, but after clicking the confirm dialogue box it disappears. Different parts of the A2 system grey out at times and seem to disconnect, also different errors pop up like compass calibration errors, stick configuration errors, firmware mismatch etc. The system was working perfectly well before upgrading, seems to me like fragments of old firmware are stuck in the eproms and therefore causing failures. I heard DJI has tools to flush the eproms and reinstall firmware. I tried shorting F1 and F2 ports on the controller already but to no avail.