The documentation you linked to is very out of date, we have not been making penetrators like that for some time. We’re currently in the middle of a major documentation update and move, and this is one of those things we have not gotten to updating quite yet.
We are potting almost all penetrators on the BlueROV2 right now with our Wetlink Thixotropic 80A Compound, using the technique described in the corresponding documentation. Note that the back of the penetrators is no longer potted, and it is unnecessary to do so. There is no additional potting required in the BlueROV2 assembly.
We have thoroughly tested our new compound and technique, and it is even higher performing and more reliable than the old method while being easier to pot. However, in your case it looks like a defect of some kind occurred, which is why we would like you to contact us at firstname.lastname@example.org.