Thanks guanabanus and adam!
Guanabanus, would bacterial canker or fungal disease show on one side? And thanks for the suggestion for TREC, I'll definitely do that. The side without dots was in shade and no water gets on that side, if that helps.
And Adam, it got down to the 50s and I left all my durians unprotected. There was one of the durians that I have in the greenhouse permanently that doesn't have the dots, but it has a dropper that waters it below so I don't know if that might be the reason it doesn't have the spots either, and the greenhouse wasn't heated either.