Internal Server Error

Description

I am constantly getting an internal server error in the admin center when viewing different pages. I have viewed the console when these errors appear, and it tells me the issue but i'm unsure how to go about fixing them.

Firstly an example of this, is when I go to Utilities > Updates I am getting an internal server error, and in the console it says "Failed to load resource: the server responded with a status of 403 () - /index.php?p=fitcms/actions/app/cache-updates:1"

Another example, when loading an entry, i'm getting an error that says "POST https://telent.com/index.php?p=fitcms/actions/seo/seo/render-data 403" and below that it says "Uncaught (in promise) TypeError: Cannot read property 'hasOwnProperty' of null
at e. (Snippet.js:76)
at i (runtime.js:45)
at Generator._invoke (runtime.js:271)
at Generator.e. [as next] (runtime.js:97)
at l (asyncToGenerator.js:3)
at r (asyncToGenerator.js:25)"

Do you have any ideas as to why this is happening and how to potentially fix it. Our client has reported this issue to us multiple times and is getting quite frustrated about it. I've tried updating craft in the past but has never seemed to solve the issue.

Many thanks.

Additional info

• Craft version: 3.5.19.1
• PHP version: 7.3.27
• Database driver & version: MySQL 5.5.5
• Plugins & versions: SEO plugin version - "ether/seo": "3.6.2"

Reproduce the errors in Craft 3.5.19.1 by opening Utilities > Updates and loading an entry, then inspect the console requests to fitcms/actions/app/cache-updates and fitcms/actions/seo/seo/render-data. Review the reported Snippet.js:76 error and the SEO plugin version 3.6.2; done means the affected admin pages load without the reported 403 and internal server errors.