Tvheadend

i have 3 identical dvbt and tvheadend (v. HTS Tvheadend 4.2.8-36~g5bdcfd8) recognize only 2 of them!

lsusb seems to see all of them
Bus 001 Device 008: ID 07ca:a867 AVerMedia Technologies, Inc. AVerTV DVB-T (A867)
Bus 001 Device 006: ID 07ca:a867 AVerMedia Technologies, Inc. AVerTV DVB-T (A867)
Bus 001 Device 004: ID 07ca:a867 AVerMedia Technologies, Inc. AVerTV DVB-T (A867)

while on tvheadend only 2 of them!

dmesg | grep dvb
[ 3.995622] usb 1-10.2: dvb_usb_af9035: prechip_version=00 chip_version=03 ch ip_type=3802
[ 3.995918] usb 1-10.2: dvb_usb_v2: found a 'AVerMedia HD Volar (A867)' in wa rm state
[ 3.997658] usb 1-10.2: dvb_usb_v2: will pass the complete MPEG2 transport st ream to the software demuxer
[ 4.356053] usb 1-10.2: dvb_usb_v2: schedule remote query interval to 500 mse cs
[ 4.356055] usb 1-10.2: dvb_usb_v2: 'AVerMedia HD Volar (A867)' successfully initialized and connected
[ 4.357835] usb 1-10.3: dvb_usb_af9035: prechip_version=00 chip_version=03 ch ip_type=3802
[ 4.358150] usb 1-10.3: dvb_usb_v2: found a 'AVerMedia HD Volar (A867)' in wa rm state
[ 4.359916] usb 1-10.3: dvb_usb_v2: will pass the complete MPEG2 transport st ream to the software demuxer
[ 4.719322] usb 1-10.3: dvb_usb_v2: schedule remote query interval to 500 mse cs
[ 4.719323] usb 1-10.3: dvb_usb_v2: 'AVerMedia HD Volar (A867)' successfully initialized and connected
[ 4.721024] usb 1-10.4: dvb_usb_af9035: prechip_version=00 chip_version=03 ch ip_type=3802
[ 4.721341] usb 1-10.4: dvb_usb_v2: found a 'AVerMedia HD Volar (A867)' in wa rm state
[ 4.723120] usb 1-10.4: dvb_usb_v2: will pass the complete MPEG2 transport st ream to the software demuxer
[ 5.074576] usbcore: registered new interface driver dvb_usb_af9035

do i have to set something on tvheadend?