Plugin trackserver can’t upload gpx files

Hi, I’m using:

PHP 7.0.18-0ubuntu0.16.04.1
mysql Ver 14.14 Distrib 5.7.19
WordPress 4.8
and the newest Trackserver Version from the WordPress appstore Version 3.0.1

I installed your Plugin and i think its great. Thank you very much.
I tried livetracking with trackme and OsmAnd it works fine.

But when i try to upload a gpx-track from my Mobile phone or my laptop it ends in a white screen without any errormessage.
I’m clicking upload file, select a file and after clicking the button upload file the white screen comes up.

Next problem i have is: I don’t know what happens to the pictures i made with trackme. It semms as if they were uploaded too, but i cant see them anywhere in wordpress and markers i set won’t appear on the map.

Last thing is that i cannot offer a track for downloading. If i use the tslink statement (i copied it from your website and changed the track id) i can click the link but nothing happend.

Thanks for your work and for your help.

Kind regards

Leo Macke