problem with setting up appointment+

Hi, I´m a solopreneur offering consulting via phone (30/60/90 min) or on site (210/420 min). I set up 1 or multiple service(s) for each duration and 1 dummy service provider for each duration. I´m aiming at offering 30/60/90 durations only on Thursdays (5-7pm) and Fridays and set up the working hours for the respective service providers. 210/420 durations are also set up with Monday through Thursday (until 4pm).

My problem:
with this setup:
[app_service_providers select="bitte wählen"]
[app_services select="Ihre Buchungsmöglichkeiten" order_by="duration" show="Verfügbarkeit anzeigen"]
[app_schedule title="Kalender vom START bis END" add="1" logged=""]
[app_pagination step="1"]

the weekly calendar is shown, but in the dropdown field for service providers only 1 service provider is listed.

Help appreciated; support access is granted. Thanks a lot!