OK, so I tried ripping the DVD with my usual software (DVDvob2mpg, which should just repackage the video instead of transcoding it).
A. The video is now corrupted for some reason, in both MPC and SMPlayer with SVP off
B. But I get the exact same behavior in SMPlayer. Black screen with SVP on, normal video with SVP closed or the "temporarily disabled" checkbox checked.
Might be something to do with how the video is encoded. It's definitely interlaced, if that matters.
Log from SMPlayer, then MPC:
17:19:00.701 [i]: VideoPlayer: mpv connected, waiting for the video info...
17:19:00.801 [i]: VideoPlayer: mpv git-a4a2649
17:19:00.926 [i]: Media: video 720x480 [PAR 0.889] at 29.970 fps [constant]
17:19:00.928 [i]: Media: scan type is interlaced, assuming 59.940 fps instead of 29.970 fps
17:19:00.928 [i]: Media: codec type is MPEG Video, YUV/4:2:0/8 bits
17:19:00.928 [i]: 4492 0
17:19:01.200 [i]: Playback: starting up...
17:19:01.200 [i]: Playback [7a1dc859]: Frame server (64-bit) C:\Program Files (x86)\SVP 4\mpv64\vapoursynth.dll
17:19:01.203 [i]: Playback [7a1dc859]: resulting video frame 720x480
17:19:01.204 [i]: Playback [7a1dc859]: 1 acceptible profiles, best is 'Automatic' [0]
17:19:01.204 [i]: Playback [7a1dc859]: enabled while video is playing
17:19:01.204 [i]: Profile: using auto values [1]
17:19:01.209 [i]: Playback: playing at 59.94 [59.94 *1/1]
17:19:26.276 [E]: QWindowsPipeWriter: GetOverlappedResult failed. (The pipe has been ended.)
17:19:40.333 [i]: Playback [7a1dc859]: disabled while video is playing
17:20:13.042 [i]: Playback [7a1dc859]: deleted
17:20:33.583 [i]: 396 328606
17:20:33.584 [i]: VideoPlayer: new ffdshow video [50320] in mpc-hc64.exe (64-bit) [MPC-HC 1.7.10.0] on screen 0
17:20:33.718 [i]: Media: video 720x480 [PAR 0.889] at 29.970 fps [constant]
17:20:33.719 [i]: Media: scan type is interlaced, assuming 59.940 fps instead of 29.970 fps
17:20:33.719 [i]: Media: codec type is MPEG Video, YUV/4:2:0/8 bits
17:20:33.719 [W]: Media: frame rate info can be incorrect - 29.970 fps via ffdshow vs. 59.940 fps via MediaInfo
17:20:33.720 [i]: VideoPlayer: clear AVS script previously set by SVP
17:20:33.721 [i]: Playback: starting up...
17:20:33.721 [i]: Playback [50320]: Frame server (64-bit) 0.1.0.0, AviSynth+ 0.1 (r1779, MT, x86_64), C:\WINDOWS\SYSTEM32\avisynth.dll
17:20:33.724 [i]: Playback [50320]: resulting video frame 720x480
17:20:33.724 [i]: Playback [50320]: 1 acceptible profiles, best is 'Automatic' [0]
17:21:05.171 [i]: Playback [50320]: enabled while video is paused
17:21:05.171 [i]: Profile: using auto values [1]
17:21:05.179 [i]: Playback: playing at 59.94 [59.94 *1/1]
17:21:17.777 [i]: Playback [50320]: seek was detected - turning off and back on...
17:21:17.844 [i]: FFDShow: remove instance [50320]
17:21:17.844 [i]: Playback [50320]: disabled while video is stopped
17:21:18.179 [i]: Playback [50320]: deleted