Try to do this settings from scratch, before you search for channels for the first time (uninstall the Tvheadend server Add-on including settings, install it again). Disable the unneeded adapters and perform the MUXes configuration from Tvheadend.
Consider a manual settings for just the MUX8 as outlined in post #2.
Create a Network with just that single MUX, set the Frequency to 184500000, then you may need to play with Bandwith (probably 7 MHz for VHF) and Constellation. Then run Force Scan for the Network.
BTW. you can also try to set the fixed adapter number for Astrometa before you start configuring Tvheadend:
echo options dvb-usb-rtl28xxu adapter_nr=5 > /storage/.config/modprobe.d/astrometa.conf
Reboot LE to activate it.