Thanks for giving the example plugin a try. I regret that it’s not working for you.
I have never seen a “405” error with this plugin. It looks like some sort of hosting problem. If the actual message is “Method Not Allowed” it might be coming from WordPress but I do not see exactly how or where.
If you do an internet search for “http 405 wordpress” you will see many articles that suggest solutions. Some of them require significant work, but here is one simple solution you can try:
wp-comments-post – HTTP ERROR 405
Here is one typical article example:
Fixing the 405 Method Not Allowed Error on WordPress
Other articles suggest looking at the “Site Health” report; you can find that on the admin mode Dashboard.
You can try one other experiment to see if the problem is specific to the “ALT from item” tool. Try scrolling to the bottom of the MLA Insert Fixit page and clicking the “Refresh Caches” tool. If that works, try the “ALT from item” tool again within a few minutes.
40,000 records is a significant number and may require more server memory and/or script running time. Those issues should give a different error message though.
Your best course of action is to contact the support team at your web hosting company and see if they can give you more information from the site error log and some ideas on how to fix the problem. If I can help, they can contact me at my web site and I will do what I can.
Thanks for your understanding and your patience.