Hi,
I submit an issue on February, 14th to mention that tree module display nothing. A response was posted informing that issue is solved in Jdownloads 4.0.17. Apparently, it's still not solved neither in 4.0.17 or 4.0.18
Yes, I have already seen that this problem unfortunately still occurs from time to time. So in our demo installation we have pages on which it is displayed correctly but also others (e.g. start page) where this error occurs. So I will have to look at it again. :-\
Please try the attached version and post here your result!
5 users have downloaded it but none have reported their result. So it is difficult. :(