Cant play AVI / folders missing

hi everyone .Im new here so apologies if this is in the wrong area but hopefully some of you knowledgable types might be able to help me out .I upgraded to the latest Plex media server as i was tidying up all my drives so all the paths had to be changed . Now ive encountered some issues that Plex will only play MKV and MP4 on the PC , any AVI comes back with problem playing this file . This is mirrored on the TV (LG) whereby the mkv and mp4 play but the avi show three dots then time out .
Also i used to be able to access the files through tv input selection where they would just be shown as folders under plex rather than going through the actual app on the tv . I much preferred this as it was very simple and clean but now the tv input plex does not show any of the folders at all .
Sorry to ramble on but im at a bit of a loss and cant find anything on dr google .
Thanks for any help you can give me