Hello Christian
From the looks of things, it seems that your c1000 is also configured to be a querier. By default, the c1000 has the IGMP snooping querier function disabled, as stated in this Cisco Documentation. And if there is more than one querier on the subnet, it is the device with the lowest IP address that is elected as the IGMP queirer.
So my assumption is that the quireir functionality is enabled on the c1000, and its IP address is lower than that of the c9300 on that particular VLAN/subnet, and thus it is being used as the querier. To resolve the issue, you can disable the querier functionality on the c1000 by issuing the no igmp snooping querier in global configuration mode on the c1000.
Let us know how you get along!
I hope this has been helpful!
Laz