SVN revision numbers from svn:externals property, which are a multiple of 1024 (2^10), are transformed by SubGit to contain a binary suffix (“k”, “m” and “g” have been checked) in .gitsvnextmodules file.
These aren’t valid revision numbers in SVN either.
Examples:
1024 → 1k
2048 → 2k
1048576 → 1m
1049600 → 1025k
1073741824 → 1g
Noticed with Bitbucket SVN Mirror plug-in, but also tested with the latest SubGit CLI version 3.3.16.