Step to reproduce:

1. Download and setup supported version eclipse for the OS platform. Eclipse: Version: 2021-06 (4.20.0)
2. Download com-oracle-jmc-ide-release-timestamp.zip , jmc-supported-ide-release-timestamp.zip to a directory.
3. Start eclipse with supported boot JDK version.
4. Select menu item Help/Install New Software.
5. Click Add.../Archive... and select the archive update site were downloaded in step 2.
6. Click on "Select All" button and observer all available software could be selected.

Expected behavior:

At step #2, when users add jmc-supported-ide-release-timestamp.zip, all items in available software could be selected after users click on "Select All" button

Actual behavior:

At step #2, when users add jmc-supported-ide-release-timestamp.zip, some items in available software were not selected after users click on "Select All" button: 

Items: 
Subscription Tab
Twitter Action

G1 Page

Please refer to the video: Eclipse_Sellect_All.mp4

More information: 
When users expand all items and press "Select All" button, all items will be selected.