Plex slowness since around a month

Hi,
i use plex through my Nvidia Shield, wire connection with Synology NAS since a few years.
It always worked fine, but since a month, i see very it s very slow when I select a movie get on the description page and clic to PLAY
Same when i pause/play
this wait is veryyyy long, sometimes it even doesn t work at all
what the hell is going on ? how can i debug this ?

also the nas:32400/...Server Settings is always unavailable so i can t go inside to check any parameters

when i TOP my NAS i don't see much CPU/mem usage on the plex process
disk usage is also low