Try installing the latest LAVFilters-0.72.0-15.exe Nightly from
https://files.1f0.de/lavf/nightly/ . It looks like nev actually changed the handling of DVD subtitles on that build compared LAVFilters-0.72.0-13.exe, maybe it is related? The commit message mentions "Disable the CC output pin for DVD playback".
If that doesn't work, ensure that you've run XySubFilter regsvr32 (as admin) and it actually succeeded, and also test MPC-BE to rule out it's not just a MPC-HC quirk. The last thing you could try is setting XySubFilter to "Always Load" under Properties->Main.
Personally I've been using MPC-HC 1.7.16, madVR 90.24, LAVFilters-0.72.0-15 on Win7 and and don't remember seeing anything like that.
Though thinking back, I don't think XySubFilter has ever supported rendering subtitles directly from a DVD disc(?). Isn't that usually handled by DVD Navigator and a DVD/MPEG2 decoder? Is the situation differ on OS newer than Win7? LAV Splitter never loads for DVD playback on my end, and XySubFilter never connects to the DVD subtitle pin, the subtitle pin is always taken and rendered by the video decoder.
If there is some kind of weird timing conflict going on, media players should probably consider blocking XySubFilter when a DVD disc is played. Yet it is curious if it doesn't occur with older madVR builds though, so maybe it's something madshi could fix on his end?