There’s a method to force interface links to only negotiate on GbE in OpenWrt but IDK if that conflicts with GL’s customizations for the Opal. I’d be hesitant to try it given @hansome & @alzhao would be better suited to give insights here of course.
Of course I’m assuming at least one of the connected client’s interface cards can run GbE. I’ve seen Realtek GbE NICs only capable of pushing 600 Mbps… on a good day. OP, do you happen to have a card that features TOE?
In the mean time it might be worth pulling a backup just in case: