That may work, depending on what the other side is, and how the files got stored on "that other side".
In this case it is probably because CIFS assumes Windows at the other side (so it uses cp437 instead of utf8 ), but you use a Linux server running Samba (in this case from Synology) which probably defaults to utf8, being linux.
Indeed, Synology uses UTF8 by default (My file name is garbled. What can I do? - Synology Kunskapscenter). As explained in the article (The Purpose of iocharset=utf8 in Mounting Windows SMB Shares to Linux | DeviceTests), it seems Linux uses the iso8859-1 character encoding for mounts. Note also that I'm not using mount manager (maybe mount manager adds iocharset=utf8 ?). But if other folks are facing similar issue, this is the way to go.