Why can't ffmpeg convert mkv file?

Question

fmpeg

In general, I downloaded some series in mkv format, when I try to convert it to mp4, it gives this:
[matroska, webm @ 0x8304a0] Read error at pos. 2241497 (0x2233d9)
What is this all about? the file itself is played ... I tried to ignore damaged / incorrect frames, but as a result the file is generally small in size ... something is not right