Hmmm... just did the update to 2.4.0+build.2019.02.26.22.55.37.89e45ac33
And after updating, I saw that our Kunena forum user avatars were all missing.
I had a look and found that our plugin 'Kunena - Community Builder Integration' was disabled.
Enabled it and all is well.
But is that normal? ( I never noticed this behavior before...)