I have the same problem on Mint 19.2, wine works fine, (or for example winecfg), but in POL unlisted sofware install, the supposed winecfg and later the software installation window is a small box, only displays the resizing corners. All the wine windows are like this.
Whatever software I want to install, I am stuck at this point every time. It does the same with the wine 1.7.x/32 I want to use in my case, but the system version does the same too, which is fresh, 3.6 if memory serves... I already reinstalled POL and wine completely, removing all my settings renaming the hidden dirs for a tryout, same.
I tried the above method by HADSOX, tried an older including removing the zlib files, which leads to an error message. So, I tried everything I found on google as "playonlinux window invisible". All I found was at least 1 year old, so to me it seems to be an already solved problem. I even found a 2 year old link to a solution on the POL site, which is 404 now: https://www.playonlinux.com/en/issue-5476.html