Submenu tree problem
I have managed to fix this issue by reverting the module to an older version.As I see in the release notes 


  Issue #3037177 by itcrowd72, omrmankar, troybthompson: PHP 7.2 each() function is deprecated


The php version I am still using is 5.6. It looks like the new module version is not ok with 5.6, or at least with my setup.