MB Pro is eating or dropping folders on external storage drives

MacBook Pro 15-inch, mid 2012

2.3 ghz i7 chip

16 gb memory

Apple advised I upgrade to Mojave, because my MB Pro has been eating folders on my external storage drives... I store large video files on 4 TB external drives. I have 3 such drives for redundancy, no RAID system, just manual transfers for now. Western Digital EasyStore and My Passport drives. I bought sturdy EasyStore drives with dedicated power supplies because the little cheapies always give connection problems and disconnect too easily, with the slightest bump. But I'm having problems now with all external drives.

Transferring files around, I get fault indications, "Operation could not be completed... External drive disconnected" etc, at the slightest touch... Then, entire folders vanish, off the hard drives. However they are still there---the storage stats, gig quantities don't change---the folders just become invisible.

I called Tech Support and we tried to do Repair on the drives in Disk Utility. The First Aid features were grayed out/not available. Apple advised to switch to Mojave. I did that, but still, the hard drives are corrupted: entire large folders of data are still invisible---but somehow still there, because the storage stats have not changed.

And Disk Utility still has the First Aid option grayed out. Hoping someone, somewhere, has some ideas on how to recover this data. I have one drive left uncorrupted---I hope---but I'm afraid to hook in to it now, if it goes, tons of unrecoverable data will be lost.