What were some discussed and current potential issues with pre-forked Bitcoin coins from August 2017 that have never moved since then? I was speaking to a friend that mentioned that there were issues with pre-forked Bitcoin coins from Aug 2017 that never moved. He wouldn't tell me exactly what the potential issue was, but what were some discussed or potential issues with these unmoved pre-fork UTXOs?
Is it a potential double spend that could happen on these coins that never moved?
No, there is no such problem. When BCH developers thought about introduction replay protection, they first agreed on the OP_RETURN-based one. Then they changed their minds and decided to use the better SIGHASH_FORKID-based one (see details about BCH replay protection).
Their first replay protection wasn't removed. It expired with block 530,000. After that block, unless you had moved your coins, it would have been impossible to separate your coins using that method.
That didn't matter to anyone then, since the second replay protection method introduced was made mandatory and worked perfectly. It was actually good enough to be exemplary (Bitcoin Gold copied it).

If you have pre-2017 coins, then you have BTC, BCH, BCHA, and BCHSV. To split those, send your bitcoins and BCHs to Coinex and they'll split it for you. (It is suggested to check that your transactions don't have nLockTime.)