Haven't used plugin ... have already done my clean up of users for beginning of this academic session ...
In your screen shot the 2030 number ... is that the number of users?
Plus there are some tabs ... what info do they provide. And what happens if one uses the 'Append ....' link?
From the readme about plugin, it uses the event logs ... logstore_standard_log? ... to retrieve deleted user info. That table is normally one of the the largest tables if not *the* largest table so yeah, can comprehend the warnings about time.
You might need to attempt to get answers via:
https://moodle.org/plugins/tool_userrestore
In the comments of above or by contacting the maintainers seen on the page above.
'SoS', Ken