This one is puzzling for me because at one point, this bug was identified in 2014:
/plugins/system/t3/includes/joomla3/pagination.php
Then this file started "firing" - even though the site is still Joomla 3:
/plugins/system/t3/includes/joomla4/pagination.php
Solution / Fix / Procedure:
1. Disable that problem file by renaming it:
/plugins/system/t3/includes/joomla4/pagination.php
(sanity check: refresh the page and your pagination CSS styles will disappear)
2. Add this template override file to your template directory, e.g:
/templates/ts3_base_blank/html/pagination.php
(sanity check: refresh the page and your pagination CSS styles will be back)
3. Go into Components -> sh404sef -> URL's -> Filter/search by "page-" -> Delete with Duplicates
(sanity check: refresh the page and this will force sh404sef to rebuild those URL's... your pagination will work correctly now, too!)
Additional:
You might need to re-apply Step 1 after future updates to the T3 Framework plugin.
