With the latest release (v1.6.0.beta4) there seems to be a problem with the topic list?
Here my local installation with v1.6.0.beta4:
However, the problem does not occur on the latest master commit (currently 628773258e244f924823662c141c2381f8b0b79d):
You can also reproduce it on our hosted instance “forum.plentymarkets.com” which has the v1.6.0.beta4 deployed.
I am also using the Topic List Preview Plug-in which seems also to be broken on v1.6.0.beta4.