Ipad 12.9 (3rd gen) v.14.7.1(18G82)
Artstudio Pro v. 3.2.7(691)
In Short: After opening and saving/closing artstudio files, the Ipad storage keeps increasing. Doesnt matter whether the app is closed, or the ipad rebooted, the storage isn't being freed up. Probably the app doesnt purge the "temporary save" files mentioned in this thread by LuckyClan https://www.luckyclan.com/forum/index.php?topic=2054.msg5434#msg5434
"Save is implemented in Artstudio in a "safe" way - it first saves everything in a temp package, then move the whole packed to destination."
I managed to reproduce the same behaviour after resetting the ipad and resaving art studio files until the storage filled up and the app had to be deleted/ipad reseted/restored again.
In Detail: One day i got a warning that my 64 gb ipad was running out of storage, rebooting ~15 times and offloading all apps didnt work to free up that space (the moment other apps were offloaded or deleted, the freed up space would be filled up mysteriously again (because i had artstudio opened as i was backing up my files just in case), this prevented the ipad from allowing to delete individual files as it needed storage to do that, or to even backup the ipad on itunes since the ipad needs storage for that too). I deleted apps one by one until deleting Artstudio (NOT OFFLOADIND) with all its art files, or erasing all data with Ipad reset did the trick. Ive succesffully managed to backup and restore all my files since then and managed to replicate the same behaviour again by opening, modifying and closing/saving artstudio files again until the storage filled up and nothing but deleting art studio or reseting the ipad to factory settings worked.