ffmpeg unable to use specific 3dlut file

[Bernie]

Hi there,

I have some D-log M video files from my DJI Mavic 2 drone that I would like to process on my linux system in Openshot. In order to apply a 3d LUT I use ffmpeg with the option -vf lut3d=<LUT file>. However using a default LUT file provided by DJI results in a error. PLease help!

Summary of the bug:
How to reproduce:

% ffmpeg -i input.mp4 -vf lut3d="DLog-M+to+Rec709.cube" output.mp4
ffmpeg version 3.4.6-0ubuntu0.18.04.1
built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)

The output of ffmpeg is:
[Parsed_lut3d_0 @ 0x55fd3ad23e20] 3D LUT is empty
[AVFilterGraph @ 0x55fd3ad21c20] Error initializing filter 'lut3d' with args 'DLog-M+to+Rec709.cube'
Error reinitializing filters!
Failed to inject frame into filter network: Invalid data found when processing input
Error while processing the decoded data for stream #0:0
Conversion failed!

I have an other LUT file (thisoneworks.cube) that does work as expected when applied to the same video file, so I'm wondering what's going wrong here.

[Bernie]

the LUT file that causes ffmpeg to exit with error

[Bernie]

Other LUT file that ffmpeg processes correctly

[Elon Musk]

Use recent ffmpeg 4.2. This was already fixed.