@daspy:
After having fixed the PCM-WAV header, it seems that after 4'55'' there is data corruption.
In other words, playback isn't stalling (as originally suspected by me) but the recorder appears to have recorded the same sample multiple times to the SD card. Which would explain why the file is so big (4.2 GiB).
It's exactly the same picture when I try to load the RAW file into Samplitude.
Cf. the screenshots below. Do you still want me to send you the WAV or FLAC file with the fixed header even though the problem is a lot more fundamental?