Thanks. I'm willing to try whatever it takes but not knowing Docker at all, I'm afraid it will be complicated for me to install the Joplin Server on my NAS. But if it can solve my slowness problems then it might be worth it. On the other hand, I don't know how to go about duplicating my profile, a simple copy and paste, a backup restoration, an export import?
I'm so disappointed, everything was going so well before activating the sync 
Since then, Joplin has been unusable for me and I wonder if I will be able to continue using it