I don't think it's related to heat or the spinning fans. The epoxy is way too hard for that. I'm thinking about the time the board was in the factory at the time the heatsinks were installed. The epoxy had to be soft once to attach the heatsinks on.

And then:
- The machine installed the heatsink like this.
- The machine wasn't configured properly and touched the heatsinks just after assembling them.
- The epoxy is a tad different, didn't 'hard' quickly enough on which the heatsinks moved when the fan was installed or if the fan was already there, the plug was plugged in.

Well, that's something I all assume .