[VTM GO] Failing decryption at higher resolutions and missing subtitles

[Flippi]

I would like to understand why decrypting certain streams on VTM GO is not working.
This concerns, for example, the stream on https://www.vtmgo.be/vtmgo/escape-room~b7fc1de4-d993-4c1a-af61-0d2248ba2788.
Access to the site is free, but you need an account (login details attached) and probably also a VPN connection for Belgium.

I got the kid-key combinations via WidevineProxy2 and I use mp4decrypt because shaka-packager couldn't decrypt any resolution.
yt-dlp -F --allow-unplayable-formats <url.mpd> provides the following information:

ID EXT RESOLUTION │   TBR PROTO │ VCODEC        VBR ACODEC      ABR ASR MORE INFO
───────────────────────────────────────────────────────────────────────────────────────────────────────
6  m4a audio only │  192k dash  │ audio only        mp4a.40.2  192k 48k [nld] DRM, DASH audio, m4a_dash
5  mp4 412x232    │  600k dash  │ avc1.64000D  600k video only          DRM, DASH video, mp4_dash
4  mp4 640x360    │ 1054k dash  │ avc1.64001E 1054k video only          DRM, DASH video, mp4_dash
3  mp4 960x540    │ 1871k dash  │ avc1.64001F 1871k video only          DRM, DASH video, mp4_dash
1  mp4 1280x720   │ 3506k dash  │ avc1.64001F 3506k video only          DRM, DASH video, mp4_dash
2  mp4 1920x1080  │ 5140k dash  │ avc1.640028 5140k video only          DRM, DASH video, mp4_dash

Or with N_m3u8DL-RE:

> [ ] Basic
    [X] Vid *CENC 1920x1080 | 5140 Kbps | 2 | 25 | avc1.640028 | 1274 Segments | ~01h24m46s
    [ ] Vid *CENC 1280x720 | 3506 Kbps | 1 | 25 | avc1.64001F | 1274 Segments | ~01h24m46s
    [ ] Vid *CENC 960x540 | 1871 Kbps | 3 | 25 | avc1.64001F | 1274 Segments | ~01h24m46s
    [ ] Vid *CENC 640x360 | 1053 Kbps | 4 | 25 | avc1.64001E | 1274 Segments | ~01h24m46s
    [ ] Vid *CENC 412x232 | 600 Kbps | 5 | 25 | avc1.64000D | 1274 Segments | ~01h24m46s
  [ ] Audio
    [X] Aud *CENC 6 | 192 Kbps | mp4a.40.2 | nld | 2CH | 1274 Segments | ~01h24m46s

Decrypting the stream with mp4decrypt only works at a resolution of 960x540 or lower. Other programs (but not all) on the same streaming platform can be downloaded successfully at the highest resolution offered.
How can I download and decrypt the highest resolution of the movie at the link provided above?

And what about subtitles? The film has subtitles that can be turned off in the player on the website, but they are not detected by the downloader (yt-dlp or N_m3u8DL-RE). Is there any way I can download them?

[ytdlhelp]

With OpenWV and Android CDMs at least, 540p is the maximum available resolution. For higher, maybe L1 is required. The website has some PlayReady-related code, but it seems it doesn't work correctly and requests to its endpoint with pyplayready-generated request return nothing.