Losing CSS Client Extensions when navigating to different page settings tabs and saving

Issue

CSS Client Extensions are being lost when navigating to a different tab in page settings and saving changes.
This can be reproduced with the following steps
Steps to reproduce
1. Start a clean bundle of Liferay DXP 7.4 U82
2. Enable private pages
  1. Open the Global Menu (Global Menu), go to the Control Panel tab, and click System Settings.
  2. Go to Release Feature Flags.
  3. In the Disabled Features dropdown menu, select Disable Private Pages.
  4. Click Update.
3. Add a Theme CSS Client extension
  1. Open the Global Menu (Global Menu), go to the Applications tab, and click Client Extensions.
  2. Click the Add icon and select "Add Theme CSS"
  3. In the Name field, type "Named Theme CSS Extension".
  4. Click Publish.
4. Go to the Liferay DXP site > Site Builder > Pages and select the gear icon next to Public Pages
5. On the Design tab, scroll down to the Customization section and select the "Named Theme CSS Extension" as the Theme CSS option and save.
6. Refresh the page and confirm that the "Named Theme CSS Extension" selection was saved.
7. Go to the SEO tab and without editing anything on the SEO page, click Save.
8. Go back to the Design tab and scroll down to the Customization section.
Expected behavior: The "Named Theme CSS Extension" appears as the Theme CSS option.
Actual behavior: The "Named Theme CSS Extension" does not appear as the Theme CSS option. Instead, we see "No theme CSS client extension was loaded".

This is a known issue that has been identified and addressed with LPS-191305
It will be eventually be added to a future released Update, but if a fix for this issue is needed sooner, a Support ticket can be opened and a hotfix can be requested that includes this fix.