problem with mpv_thumbnail_script from git

I’ll try in lubuntu 20.04 to use mpv_thumbnail_script
my config for this skript

cat .config/mpv/lua-settings/mpv_thumbnail_script.conf 
#Für Vorschaubildchein in mpv
cache_directory=/home/alex/mpv/my_mpv_thumbnails
autogenerate=yes
prefer_mpv=yes
mpv_no_sub=yes
disable_keybinds=yes
thumbnail_width=200
thumbnail_height=200
thumbnail_network=no
thumbnail_count=150
min_delta=5
max_delta=90

My config for mpv

cat .config/mpv/config
#hwdec=vdpau
#vo=vdpau
fullscreen
sub-scale=1
osc=no

But when i start mpv the thumbnails are black.

starting from terminal gives

mpv jd2/downloads/Aang & Tenzin - Clip_ Avatar The Legend of Korra/Aang & Tenzin - Clip_ Avatar The Legend of Korra (360p).mp4 
[mpv_thumbnail_script_server] lua-settings/ is deprecated, use directory script-opts/ 
[mpv_thumbnail_script_client_osc] lua-settings/ is deprecated, use directory script-opts/ 
 (+) Video --vid=1 (*) (h264 624x352 24.000fps)
 (+) Audio --aid=1 --alang=eng (*) (aac 2ch 44100Hz)
[vaapi] libva: /usr/lib/x86_64-linux-gnu/dri/iHD_drv_video.so init failed
Using hardware decoding (vaapi).
AO: [pulse] 44100Hz stereo 2ch float
VO: [gpu] 624x352 vaapi[nv12]
AV: 00:00:00 / 00:01:29 (0%) A-V:  0.000
[mpv_thumbnail_script_client_osc] The 'tick' event is deprecated and will be removed.
AV: 00:00:00 / 00:01:29 (0%) A-V:  0.000
[mpv_thumbnail_script_server] Thumbnailing command failed! 
[mpv_thumbnail_script_server] mpv process error: nil 
[mpv_thumbnail_script_server] Process stdout:  
[mpv_thumbnail_script_server] Debug log: /home/alex/mpv/my_mpv_thumbnails/Aang  Tenzin - Clip_ Avatar The Legend of Korra 360p-3829920/000000.bgra.log 
[mpv_thumbnail_script_server] Output file missing! /home/alex/mpv/my_mpv_thumbnails/Aang  Tenzin - Clip_ Avatar The Legend of Korra 360p-3829920/000000.bgra 
(Paused) AV: 00:01:29 / 00:01:29 (100%) A-V:  0.000


Exiting... (End of file) # here dies mpv
[mpv_thumbnail_script_client_osc] 
[mpv_thumbnail_script_client_osc] stack traceback:
[mpv_thumbnail_script_client_osc]       .../.config/mpv/scripts/mpv_thumbnail_script_client_osc.lua:1080: in function 'prop'
[mpv_thumbnail_script_client_osc]       mp.defaults:392: in function 'handler'
[mpv_thumbnail_script_client_osc]       mp.defaults:486: in function 'call_event_handlers'
[mpv_thumbnail_script_client_osc]       mp.defaults:520: in function 'dispatch_events'                                                                     
[mpv_thumbnail_script_client_osc]       mp.defaults:479: in function <mp.defaults:478>                                                                     
[mpv_thumbnail_script_client_osc]       [C]: in ?                                                                                                          
[mpv_thumbnail_script_client_osc]       [C]: in ?                                                                                                          
[mpv_thumbnail_script_client_osc] Lua error: .../.config/mpv/scripts/mpv_thumbnail_script_client_osc.lua:1080: attempt to compare nil with number 

I’m not sure, if i made a mistake, or something is wrong with the scripts itself.

log file

Note: I can not skript.
I found this this question and followed the link in the answer, but I do not know what I have to do.

.config/mpv/lua-settings/mpv_thumbnail_script.conf 

prefer_mpv=yes

prefer_mpv=no