Thank you for your reply.
I made a mistake in the debugging process – it is rather a combination of conflicting plugins and a memory issue (maybe my host ?) and has nothing to do with amr-users.
– amr users does not conflict itself with Fusion builder (and yes, it is Avada theme).
– but amr + s2members makes Fusion builder grey.
– nonetheless, s2members alone makes it work.
I mistakenly thought that amr was involved.
I realized too that some other combination of plugins did the same with s2members (when combined). So it may be definitely something related with this plugin s2members (I’ll write them).
Olren