I have also posted a ticket, wanted to check if anyone else is having a similar problem.
Trying to clone any site is immediately errors out with:
“Creating backup on %1$s expected size: %2$dMB (estimated time: %3$d seconds). Child plugin is disabled or the security key is incorrect. Please resync with your main installation.”
Both sites using the latest version of the child plugin. Resyncing both sites makes no difference.