While it seems the development of the megatools is in hiatus, looking at the official git, there is an issue that would require a fix.

Version: megatools 1.11.0
Problem: Randomly uploading, copying will be halted on various error messages, such as:
megaput --username user@email --password passphrase file_yet_the_larger_the_file_is_the_more_likely_upload_will_fail.ext
file_yet_the_larger_the_file_is_the_more_likely_upload_will_fail.ext: 100.00% - done 6.9 GiB (avg. 9.8 MiB/s) of 6.9 GiB (0 bytes/s)
ERROR: Upload failed for 'file_yet_the_larger_the_file_is_the_more_likely_upload_will_fail.ext': API call 'p' failed: HTTP POST failed: CURL error: SSL connect error

More information regarding this specific error:
https://github.com/megous/megatools/issues/462