Turns out that the wallet is hard-coded by default to use segwit addresses and on a non-upgraded network, coins sent to segwit addresses are lost.

Don't use the 0.16.3 client, revert to either the 0.8.6 client or the Crossverse 0.15.99 client.

I've withdrawn the 0.16.3 release and deleted the repository as it's clear that supporting this particular upgrade is beyond my skillset.

If you have coins stuck on segwit addresses, PM me with the relevant 0.16.3 client privkey and I'll replace your coins.

Sad but true.

Cheers

Graham