I vaguely remember that 10 or 15 years ago I've seen obscure ssh client for relatively obscure platform that could not handle RSA keys that were longer than som

I vaguely remember that 10 or 15 years ago I've seen obscure ssh client for relatively obscure platform that could not handle RSA keys that were longer than some X, with X being something like 640. Even then, generating such key with OpenSSH was not something one could do by accident.