I am not sure, but the problem might be not suffitient memory in system partition.
You wrote you had moved fonts and dictionaries (I guess to system partition). I do not know how much memory you used there, but maybe too much.
There is an script in M92 (and most probably also in Firefly) that checks on startup amount of free space in system partition and if it is below certain treshold it erases some "unneeded" data, like settings, recent documents, maybe also bookmarks...
Try to move dictionaries back to user partition. There is no need to have them in system partition, it is much better to have them user partition (less work to install, easier to maintain, ...).
Maybe that the same is the truth for fonts, but I am not sure...
If this is not the cause, then it might hardware problem.