Using Press It bookmark gives 406 error sometimes

Using the Press it bookmark to add a post sometimes results in a

“Not Acceptable
An appropriate representation of the requested resource /wp-admin/post.php could not be found on this server.”

error. I have seen a lot of similar posts but no solution (unless you call ‘probably a server error’ a solution.

The URL I am posting is https://www.theinquirer.net/?article=28201

The URL for editing the post – generated by the bookmarklet is

https://don.robertson.net.nz/wp-admin/post.php?text=&popupurl=http%3A%2F%2Fwww.theinquirer.net%2F%3Farticle%3D28201&popuptitle=Open%20Source%20databases%20rounded%20up%20and%20rodeod

If I change this URL to

https://don.robertson.net.nz/wp-admin/post.php?text=&popupurl=http%3A%2F%2Fwww.theinquirer.net%2FFarticle%3D28201&popuptitle=Open%20Source%20databases%20rounded%20up%20and%20rodeod

that is, if I take out the %3F (?) in the popupurl=http%3A%2F%2Fwww.theinquirer.net%2F%3Farticle%3D28201 (popupurl=https://www.theinquirer.net/?article=28201) part of the URL, it works.

Seems there could be a problem with /? in the URL?

Don