That’s strange. I’m using the old Jellyfin addon (not the JellyCon), and so far only encountered one bug in total, which, if you are familiar with kodi addon ecosystem, is basically unheard of. And even that one is related to my non-standard manual configuration that allows me to use WebDAV instead SMB or NFS. It’s using the wrong type of escaping for certain special characters, which is understandable, because who in their right mind uses WebDAV?
Yes. Jellyfin will index the media files and push all the metadata along with the file paths on the network share they both can see to the local kodi database. That way browsing the library on kodi does not suffer any additional latency, but you also lose some advanced jellyfin functionality like on the fly re-encoding.