which version of windows are you on? Its possibly cleanup is run occasionally and its deleting your temp files over a certain age - the new version of win 10 has such a feature, but you have to turn it on I think. SSD deletes files as soon as you do so its not TRIM
setting off, though it probably uses TRIM to do the operation.
gaining 70gb is a big jump though, if you gain so much back each time I would think to run cleanup more often to not get so close to full.