Plugin doesn’t work for me anymore?

I’ve been using TablePress for a while without any issues, but now I have come across (at least) three problems:
1. Whenever I save information to a existing table, I get this message:

Saving failed: AJAX call failed: error – . Try again while holding down the “Shift” key.
– When I click on the shift key while saving, I get:
403 Forbidden
Permission denied. Our sentries tell us that you should not be here.

2. When I tried copying a table, it sends me directly to that 403 page.
3. When I tried creating a new table, after giving it a name and amount of columns/rows, I’m also sent to the 403 page.

Any help with this will be appreciated!

Debug and version info:
· Website: https://tourstoyou.org
· TablePress: 1.10
· TablePress (DB): 39
· TablePress table scheme: 3
· Plugin installed: 2018/08/10 15:18:51
· WordPress: 5.3.2
· Multisite: no
· PHP: 7.2.26
· mysqli Extension: true
· mySQL (Server): 5.5.5-10.3.21-MariaDB-log
· mySQL (Client): mysqlnd 5.0.12-dev – 20150407 – $Id: 3591daad22de08524295e1bd073aceeff11e6579 $
· ZIP support: yes
· UTF-8 conversion: yes
· WP Memory Limit: 256M
· Server Memory Limit: 256M
· WP_DEBUG: false
· WP_POST_REVISIONS: true