I would suggest on the retraction cycle
I'm thinking retraction cycle as well. Didn't the crew report a problem with the gear after departure & that was the reason for the return?
The door could have been closing before the gear was fully retracted, leading to it being powered into the gear, jamming everything. Then, when the alternate gear extension was done for the wing gear, it didn't move.
The other thing that got my attention in the photo is the absence of the aft, outboard wheel. It is on the same fore/aft axis as the forward, outboard wheel, which is the one that is visible. So shouldn't it be at least partly visible in the photo? Has this wheel separated from the aircraft & is damage from the loss of this wheel the reason for the gear jamming?