Thank You Like - Recount very slow

[Laird]

Do you also get an error when you run this (after replacing "YOURPREFIX" with your actual prefix)?

SHOW COLUMNS FROM `YOURPREFIX_threads` LIKE 'tyl_tnumtyls';

[...]

No error [...]

That's odd. You say that your database server is MySQL (I assume you mean that it's not the MariaDB fork), and the MySQL documentation says:

The same privileges apply to selecting information from INFORMATION_SCHEMA and viewing the same information through SHOW statements.

However, you're getting a permission error on one and not on the other. I'm not sure why.

All the tables in the db are MyISAM

OK, thanks, that's good to know. It rules out the applicability of this from the same MySQL documentation page (my clarifying addition in square brackets):

Some [INFORMATION_SCHEMA] tables have different privilege requirements; for these, the requirements are mentioned in the applicable table descriptions. For example, InnoDB tables (tables with names that begin with INNODB_) require the PROCESS privilege.

I'm still trying to figure out from here what's going on...