Nl:special:diff/60191909 (simply correcting a sorting error) shows up immediately in Wikitext, but takes endlessly in visual mode. When I switched back to wikitext diff after waiting for fifteen minutes (!) it responded immediately. A second try gave the same result.
I encountered the problem while editing in the visual mode, but clicking the diff from the history page or the link above made no difference.
The previous diff has no such issues. My computer is a chromebook with lavish amounts of memory but a slow outdated processor. The browser is Chrome of course.