Too much widgets can not drag or move

Sometime increasing memory resolves many backend issues.

Have you tried:
– deactivating ALL (yes all) plugins temporarily to see if this resolves the problem (plugin functions can interfere). If this works, re-activate them individually (one-by-one) to find the problematic plugin(s).
– If that does not resolve the issue, try switching to the unedited default Twenty Fifteen theme for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins).