Fixed gh-678 moved the compilation success message out of the redirection message to a user state message, that get loaded to the page on successful compilation. This preserves the button scripts needed to install the compiled packages.
Upgrade to Joomla 3.9.25, and install this patch. Then the compiler page should work as expected.
That JCB would work in Joomla 3.9.25 as always.
The Joomla 3.9.25 update broke the compiler page installation buttons.
Quickly upgrading JCB to the current staging branch to test this