Although not a bug, perhaps a 'design limitation' which could be easily rectified:
As mentioned in this topic, if you transfer a save game to another device and put the files into a folder corresponding to a different 'slot' number, when you load and later save this game, it will write to the original slot number which it had on the original device. It will ignore the slot number that you put it in by folder number.
This can result in data being overwritten and lost in that 'old' slot number. The 'new' slot number you transferred the save data into remains unchanged from its original state. Further details described in the linked thread above.
Perhaps the transfer of save game files is not an 'officially' supported process, but clearly quite a few people have had a need to do this operation to transfer campaign progress to a bigger screen, in the absence of any cloud-based synchronisation features.
My experience was on the latest Android version. I haven't tried to repeat it, I must admit. (After I lost my progress and was trying (fruitlessly) to re-run a few rounds of mission 2 countless times in the hope of 'recovering' back to the point I was at, I lost the will to live! )
I would love to see a cloud-sync added in the future, perhaps linked to our Asmodee/FFG accounts. The save files are only a few bytes after all.