I finally found the fix! It was indeed the Samsung's in-house "Storage Booster" app and I needed to uncheck "Auto optimise phone" and uncheck "Auto delete unnecessary data" - the latter including auto deleting log files, cache files (and probably deleting all the kml/gpx and orux db files - which are my most prized possessions!). And since it was a new phone, it had these two options checked and this auto deleting process was scheduled overnight when the phone was not in use. Thanks to one late night when I was up on my phone and caught this process happening while I was doing something else. Gosh, took me several days to finally figure it out but I am so glad it all worked out. It never happened with my old phone, and I hope it helps others in case they face the same problem in the future.
Happy hiking/birding/tracking/biking! Happy Orux-ing! Love to OruxMaps!!
Cheers!
Pu