Just conjecture on my part, but I think when a firmware update comes out that has no “functional” changes but is for production, it’s because they made a hardware revision (component change) due to parts availability/cost and updated the firmware to be compatible with the component change. But in this case, it’s causing issues when updating synths with the original design/component in it. Thus, if you have a OB-6 with older firmware, don’t update it to 1.7.6. If you buy a new one that has 1.7.6 already on board, it’s probably got whatever component/design change that necessitated the firmware change.