Failed to compile less

When trying to compile my less I get

templates/purity_iii/less/bootstrap.less File '../../../../../templates/purity_iii/less.less` not found. in anonymous-file-0.less'

I found that it is during the calculation of import files. It sees the name of the directory purity_iii/less. I think it should import all files in that directory but instead it adds a ".less" to the directory name in line 5639! of file '/plugins/system/t3/includes/lessphp/less/less.php'

Deinstalling T3 and Purity (removing t3-assets) and reinstalling T3 and Purity did not help.

BTW I saw that there are four! less compilers installed in my installation. One from joomla (I think since 3.4.x) two! from Akeeba Backup and one from T3.