Looks like contamination of the developer, possibly dried fixer crystals left in the dev tank maybe from around the seal area, these stick to the film causing tiny marks like this

Too big a change in temperatures can cause reticulation and 5 degrees C is too large a difference, should be +/- 1 degree, but this doesn't look like reticulation. Fomafilms are softer than Lodak/Ilford/Agfa but not anything like as bas as EFKE.

Ian