Subtitle micro-stutter with libVLC and weird design with ExoPlayer

[oben]

Hi, I am streaming mkv's from my Jellyfin Windows Server 10.8.12 to my Sony XR-83A90J using the Jellyfin for Android TV app installed via the Play Store.

When using libVLC I get a micro stutter every time a subtitle changes. The video runs perfectly smooth until a subtitle is displayed or changed to a new one. Exactly the second the subtitle is displayed, there is a fraction of a micro-stutter, it's only a fraction of a second, but definitely noticeable.
When I switch to ExoPlayer, this behavior stops, but the subtitles aren't white and in a really weird design, I can show a picture later.

I haven't been able to reproduce this behavior on other devices.
I don't use transcoding. Transcoding is completely disabled for this Jellyfin user, and I verified that Jellyfin is using DirectPlay for the movie.
During playback there is 0 load on the server (because there is no transcoding).

This happens with every movie, not just the one from the example below. Here is one of the smaller mkv's I have, where this issue occurs:
Video

Code:

ID : 1
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main 10@L5.1@High
HDR format : Dolby Vision, Version 1.0, dvhe.08.06, BL+RPU, HDR10 compatible / SMPTE ST 2094 App 4, Version 1, HDR10+ Profile B compatible
Codec ID : V_MPEGH/ISO/HEVC
Duration : 2 h 41 min
Bit rate : 56.0 Mb/s
Width : 3 840 pixels
Height : 2 160 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0 (Type 2)
Bit depth : 10 bits
Bits/(Pixel*Frame) : 0.282
Stream size : 63.2 GiB (90%)
Title : censored for obvious reasons
Language : English
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : PQ
Matrix coefficients : BT.2020 non-constant
Mastering display color primaries : Display P3
Mastering display luminance : min: 0.0001 cd/m2, max: 1000 cd/m2
Maximum Content Light Level : 385 cd/m2
Maximum Frame-Average Light Level : 213 cd/m2

Text #1

Code:

ID : 6
ID in the original source medium : 4768 (0x12A0)
Format : PGS
Muxing mode : zlib
Codec ID : S_HDMV/PGS
Codec ID/Info : Picture based subtitle format used on BDs/HD-DVDs
Duration : 2 h 39 min
Bit rate : 33.7 kb/s
Frame rate : 0.374 FPS
Count of elements : 3588
Stream size : 38.4 MiB (0%)
Language : English
Default : No
Forced : No
Original source medium : Blu-ray

Text #2

Code:

ID : 7
ID in the original source medium : 4769 (0x12A1)
Format : PGS
Muxing mode : zlib
Codec ID : S_HDMV/PGS
Codec ID/Info : Picture based subtitle format used on BDs/HD-DVDs
Duration : 2 h 40 min
Bit rate : 37.2 kb/s
Frame rate : 0.427 FPS
Count of elements : 4116
Stream size : 42.8 MiB (0%)
Language : English
Default : No
Forced : No
Original source medium : Blu-ray

Any ideas?