Avisynth input hangs before transcode starts

[truehd]

Summary of the bug:
Having an .avs input causes a long hang before successfully transcoding (to prores here but it seems to be encoder independent).
Log has thousands of lines of:

[rawvideo @ 000001eeb94f8240] PACKET SIZE: 8294400, STRIDE: 7680
[vost#0:0/prores_ks @ 000001eeb94f9440] cur_dts is invalid [init:0 i_done:0 finish:0] (this is harmless if it occurs once at the start per stream)

Code to reproduce:

% ffmpeg -i "input.avs" -ss 19:15 -to 19:34 -c:v prores_ks -profile:v hq -quant_mat:v 6 -pix_fmt yuv422p10le -an "output.mov"
ffmpeg version 2023-07-10-git-1c61c24f5f-full_build-www.gyan.dev

Avisynth+ version 3.7.2
Platform: Windows 11 22H2

[truehd]

zip that contains a log file with the verbose terminal output