Project Config Apply command does not work

Description

The ./craft project-config/apply command does not work properly. We have a few diffs in the Project Config, and when we want to apply them, the command does not throw any error or so, but after the Apply command, the diff is still the same on the command line, but on the web CMS https://domain/admin/utilities/project-config we do not see any diffs.

See this command line:

production:/app# ./craft project-config/diff
      structure:
        maxLevels: null
        uid: cb4c9cbe-46f5-4362-9683-d52e4246ada6
- dateModified: 1611838098
+ dateModified: 1612264284
  dolphiq_sitemap_entries:
    201841a3-809b-43c5-be30-b94f33046a76:
      changefreq: hourly
...
      contentColumnType: string
      fieldGroup: 252831be-a183-4ddb-a03e-dce04e3d8ccf
      handle: abstandStil
-     instructions: ''
+     instructions: 'Fügt einen Abstand hinzu'
      name: 'Abstand Stil'
      searchable: true
      settings:

production:/app# ./craft project-config/apply
Applying changes from your project config files ... done

production:/app# ./craft project-config/diff
      structure:
        maxLevels: null
        uid: cb4c9cbe-46f5-4362-9683-d52e4246ada6
- dateModified: 1611838098
+ dateModified: 1612264284
  dolphiq_sitemap_entries:
    201841a3-809b-43c5-be30-b94f33046a76:
      changefreq: hourly
...
      contentColumnType: string
      fieldGroup: 252831be-a183-4ddb-a03e-dce04e3d8ccf
      handle: abstandStil
-     instructions: ''
+     instructions: 'Fügt einen Abstand hinzu'
      name: 'Abstand Stil'
      searchable: true
      settings:

Additional info

• Craft version: 3.5.16
• PHP version: 7.2.34
• Database driver & version: MySQL 5.5

Start by reproducing the issue with ./craft project-config/diff and ./craft project-config/apply, then compare the result with the Project Config page at /admin/utilities/project-config. Done means applying the project config removes the reported diff and the web CMS shows the expected state.