Not had this experience myself, but 16k IPTV is going to take a long time to scan...
Suggest when you create [or edit] the network in Configuration/DVB Inputs/Networks, you make sure "Scan after creation"
and "Idle scan muxes" are unset.
Then you should be able to select some channels you want under Configuration/DVB Inputs/Muxes and scan them. Don't try too many at once.