advowson: Yes, as stated in the first response in this thread, the next step for anyone affected is to provide the broken save game in a form that Anders (or other interested parties) can download it and inspect it to see what is wrong. There is no self-service solution available at this time, in part because there is too little detail to understand what is wrong. If we knew what was failing, we might be able to give you specific steps you could follow to correct it. It may also be the case that the save is damaged, but that a DevilutionX developer has the tools to repair it.
As also discussed in posts in this thread, the GOG forums do not offer the ability to transfer this save file. You will need to provide it through some other means, such as posting it to a temporary file sharing site (and posting here a link to such download) or, if so invited, attaching it to a Github issue or e-mailing it to an interested party. I suggest not e-mailing it until specifically instructed to do so.
I am having this same issue as well, where do i find my save files? I don't see them in the install directory.