Sound and video synch

[Dave 1867]

Just edited an MP4 video using Avidemux 2.7.0
Perfect all the way through, until four minutes from the end and suddenly the audio was WAY out of synch (ahead) of the video.
Is there something I've missed here?
Why was just the last four minutes out of synch and the rest perfect?
Is there an owner/operator manual for Version 2.7.0 of ASvidemux?

[eumagga0x2a]

Are audio and video well in sync throughout the source video? If yes, can you reproduce the issue with the latest nightly available (r180504 for Windows / 180503 for Linux / 180404 for macOS)? If yes, please compress and attach the application log (admlog.txt from %localappdata%\avidemux\ on Windows) to your reply.

Why was just the last four minutes out of synch and the rest perfect?

Without access to the source video and without knowing the exact editing steps, it is impossible to guess what went wrong.

Is there an owner/operator manual for Version 2.7.0 of ASvidemux?

No, but there is a wiki (mostly severely outdated).