SRename will try to use long filenames even on filesystems that don't support them (like FFS), so on such filesystems filenames longer than the maximum allowed length (30 characters on FFS) will be trimmed by the filesystem itself.

Similar behaviour can be expected for filename comments. SRename allows for comments of up to 120 characters in length, but in the end the filesystem can reject the comment if it's too long (up to 80 characters for FFS).

Note that dos.library up to version 40 (Kickstart 3.1) doesn't allow for more than 107 characters in filenames so this limits even filesystems that allow for longer filenames than that.

CrossDos can behave erratically when renaming files that use it's filesystem. This isn't a fault of SRename or other rename programs.
Such a problem according to a user is that the last character of filenames is lost in renaming. This can be fixed by using full pathnames for renaming.
For Directory Opus 5 users:

If using the SRename button bank with a lister in Icon or Icon Action mode the lister won't update to show the new filenames when doing casing (uppercase, lowercase, togglecase) rename operations. This is probably caused by AmigaOS treating filenames in a case-insensitive way. In that case the user should update the lister manually.

When using the button bank's numbering functions that require the selection of filenames in the lister, the command line buffer can get full when the selected filenames don't fit in the buffer and this results in filenames with duplicate numbers.
One workaround for this is to set the "Max. CLL" value in "CLI Launching" settings in Directory Opus to the maximum value. This varies from 512 to 8192 for different versions of Directory Opus.
I have found out that setting this value to more than around 560 in Directory Opus 5.82 results in problems for CLI-launched programs. It's best to try to find out yourself what is the maximum value for this setting that works without problems in your setup.
It would be better to use the (SRCE) numbering operations that don't need the selection of filenames but process all the filenames in the source lister.