maps do not appear, white area

I use Trackserver exclusively to display older tracks recorded years ago. Since updating to version 5.x, only white areas are shown instead of the maps.
So far, the following has been checked:
Plugin uninstalled and reinstalled – OK
leaflet.js GET request – OK
Track data is indeed present in the Trackserver table – OK
I’m not an IT specialist, but perhaps you can still help me.
Here some more test pages: https://momtrack.de/oberpfaelzer-wald-murnthal-schwarzwihrnberg-radl-wander-kombi/ , https://momtrack.de/ingolstadt-stuttgart-mountainbike/

The page I need help with: [log in to see the link]