I'm getting reliably stuck on "Restart" (with a version under it, 17.3.0), can press that button as often as i want. Registry is correct, settings.json points to the correct path (not sure if it's intended that the settings are greyed out in the launcher after the first restart).
This is after a fresh install of D2 1.12A (and also with the 1.14D i had installed from ages ago previously) and then starting the MXL launcher installer and accepting all defaults, and then installing median via it afterwards.
There are also 3 other copies of D2 (for my other keysets) ony my drive, but those should not be an issue.
edit2: Atleast found the source of the problem (i think)
"[2017-07-14 04:05:08 +02:00] Error: Command failed: reg add "HKCU\Software\Battle.net\Configuration" /v "Diablo II Battle.net Gateways" /t REG_MULTI_SZ /d "1002\001\0realm.median-xl.com\01\0The Sin War" /f
ERROR: Access is denied."
Yes, it's running as administrator.
edit3: Really interesting, for some reason the "Set Value" permission for just the HKCU\Software\Battle.net\Configuration folder was set to deny for my profile. Setting that to allow (where it should be) fixed the problem.
edit4: It would be great if the settings the launcher applies to the registry would be reverted when it closes, so i can continue to use my other copies of D2 in battlenet.