Tvheadend

I'm suffering some pretty nasty performance issues when using TVH with a new TBS 6909X. TVH is running in an Arch VM but the same VBM worked fine with the a 6985 card. I release this is likely a driver issue but it works ok with simpler utilities and I was hoping someone could help. I started TVH with Mutex debugging enable and this is returned:
thread: mutex 0x55e36afe4560 at src/main.c:703 took 3540ms
thread: mutex 0x7faa0401f370 at src/input/mpegts/linuxdvb/linuxdvb_frontend.c:1010 took 1060ms
thread: mutex 0x55e36afe4560 at src/main.c:703 took 2120ms
thread: mutex 0x7faa0401f370 at src/input/mpegts/linuxdvb/linuxdvb_frontend.c:1010 took 1060ms
thread: mutex 0x55e36afe4560 at src/main.c:703 took 2120ms
thread: mutex 0x7faa0401f370 at src/input/mpegts/linuxdvb/linuxdvb_frontend.c:1010 took 1060ms
thread: mutex 0x55e36afe4560 at src/main.c:703 took 2120ms
thread: mutex 0x7faa0401f370 at src/input/mpegts/linuxdvb/linuxdvb_frontend.c:1010 took 1060ms
thread: mutex 0x55e36afe4560 at (null):0 took 2120ms
thread: mutex 0x7faa0401f370 at src/input/mpegts/linuxdvb/linuxdvb_frontend.c:1010 took 1060ms
thread: mutex 0x55e36afe4560 at (null):0 took 2120ms
thread: mutex 0x7faa0401f370 at src/input/mpegts/linuxdvb/linuxdvb_frontend.c:1010 took 1050ms
thread: mutex 0x55e36afe4560 at (null):0 took 2110ms
thread: mutex 0x7faa0401f370 at src/input/mpegts/linuxdvb/linuxdvb_frontend.c:1010 took 1060ms
thread: mutex 0x55e36afe4560 at (null):0 took 2120ms

The log looks a bit like this:
2019-05-03 23:35:04.200 [ INFO] mpegts: 11914H in Freesat - tuning on TurboSight TBS 6909x (Octa DVB-S/S2/S2X) #4 : DVB-S #0
2019-05-03 23:35:05.674 [ INFO] subscription: 0076: "scan" subscribing to mux "11914H", weight: 5, adapter: "TurboSight TBS 6909x (Octa DVB-S/S2/S2X) #4 : DVB-S #0", network: "Freesat", service: "Raw PID Subscription"
2019-05-03 23:35:08.944 [WARNING] linuxdvb: TurboSight TBS 6909x (Octa DVB-S/S2/S2X) #4 : DVB-S #0 - poll TIMEOUT
2019-05-03 23:35:10.312 [WARNING] linuxdvb: TurboSight TBS 6909x (Octa DVB-S/S2/S2X) #4 : DVB-S #0 - retune nodata
2019-05-03 23:35:17.052 [ INFO] mpegts: 11914H in Freesat - scan no data, failed
2019-05-03 23:35:17.052 [ INFO] subscription: 0076: "scan" unsubscribing

dmesg sample:
[ 4808.992028] i2c i2c-1: stid135_set_parameters: set pls_mode 0, pls_code 1 !
[ 4809.377128] i2c i2c-1: stid135_set_parameters: locked !
[ 4809.377132] i2c i2c-1: stid135_set_parameters: disable ISI filtering !
[ 4816.792251] i2c i2c-1: delivery_system=5 modulation=0 frequency=1400000 symbol_rate=27500000 inversion=2 stream_id=-1
[ 4816.794789] i2c i2c-1: stid135_set_parameters: set pls_mode 0, pls_code 1 !
[ 4820.484255] i2c i2c-1: stid135_set_parameters: not locked, band rf_power -17 dBm !
[ 4820.484259] i2c i2c-1: stid135_set_parameters: disable ISI filtering !
[ 4820.514916] i2c i2c-1: delivery_system=5 modulation=0 frequency=1400000 symbol_rate=27500000 inversion=2 stream_id=-1
[ 4820.517176] i2c i2c-1: stid135_set_parameters: set pls_mode 0, pls_code 1 !
[ 4824.193808] i2c i2c-1: stid135_set_parameters: not locked, band rf_power -16 dBm !
[ 4824.193812] i2c i2c-1: stid135_set_parameters: disable ISI filtering !

I think the issue might be related to this:
https://github.com/tbsdtv/media_build/issues/13

I have also seen some not too clear instructions showing use of odd LNB configs in TVH with this card (I'm currently running mode 1), eg:
https://www.tbsiptv.com/download/tbs6909x/tbs6909x_user_guide.pdf

Does anyone have any ideas on how to resolve this?