Hi, I have a very similar problem:
tvheadend 4.0.8~wily ubuntu 15.10 epggrab: Not getting any epg data at all.
I have a TBS5928 adapter USB QBOXS2 which runs perfectly OK on Windows 8.1 attached to the same PC (dual boot with ubuntu)
I have recently configured tvheadend for the first time and can view Astra-28.2E channels OK from the Play button in the configuration->dvb inputs->services tab.
I have checked the EPG configuration and am using EIT only (no internal or external grabbers)
Here's a sample output from syslog:
2016-02-08 11:30:49.392 tot: invalid checksum (len 8, errors 56)
2016-02-08 11:31:09.392 tot: invalid checksum (len 8, errors 58)
2016-02-08 11:31:29.459 tot: invalid checksum (len 8, errors 60)
2016-02-08 11:31:41.000 epggrab: UK: Freesat - data completion timeout for 11170.75H in Astra28.2EAll
2016-02-08 11:31:41.000 epggrab: EIT: DVB Grabber - data completion timeout for 11170.75H in Astra28.2EAll
2016-02-08 11:31:41.000 subscription: 000C: "epggrab" unsubscribing
2016-02-08 11:31:42.000 mpegts: 11508.5V in Astra28.2EAll - tuning on Conexant CX24116/CX24118 : DVB-S #0
2016-02-08 11:31:42.116 subscription: 000E: "epggrab" subscribing to mux "11508.5V", weight: 4, adapter: "Conexant CX24116/CX24118 : DVB-S #0", network: "Astra28.2EAll", service: "Raw PID Subscription"
2016-02-08 11:31:44.004 tot: invalid checksum (len 8, errors 1)
2016-02-08 11:32:04.001 tot: invalid checksum (len 8, errors 3)
2016-02-08 11:32:24.012 tot: invalid checksum (len 8, errors 5)
2016-02-08 11:32:44.455 tot: invalid checksum (len 8, errors 7)
2016-02-08 11:33:04.463 tot: invalid checksum (len 8, errors 9)
2016-02-08 11:33:24.442 tot: invalid checksum (len 8, errors 11)
2016-02-08 11:33:44.446 tot: invalid checksum (len 8, errors 13)
2016-02-08 11:34:04.460 tot: invalid checksum (len 8, errors 15)
.......
2016-02-08 11:41:24.460 tot: invalid checksum (len 8, errors 59)
2016-02-08 11:41:44.470 tot: invalid checksum (len 8, errors 61)
2016-02-08 11:41:52.000 epggrab: UK: Freesat - data completion timeout for 11508.5V in Astra28.2EAll
2016-02-08 11:41:52.000 epggrab: EIT: DVB Grabber - data completion timeout for 11508.5V in Astra28.2EAll
2016-02-08 11:41:52.000 subscription: 000E: "epggrab" unsubscribing
2016-02-08 11:41:53.000 mpegts: 11265V in Astra28.2EAll - tuning on Conexant CX24116/CX24118 : DVB-S #0
2016-02-08 11:41:53.116 subscription: 0010: "epggrab" subscribing to mux "11265V", weight: 4, adapter: "Conexant CX24116/CX24118 : DVB-S #0", network: "Astra28.2EAll", service: "Raw PID Subscription"
2016-02-08 11:42:00.402 tot: invalid checksum (len 8, errors 1)
2016-02-08 11:42:00.402 time: TDT - unable to update system time: Operation not permitted
2016-02-08 11:42:20.411 tot: invalid checksum (len 8, errors 3)
2016-02-08 11:42:40.400 tot: invalid checksum (len 8, errors 5)
...... etc....
This is repeating for all the channels similarly.
Does this help. I thought would add my problem to yours here rather than raise a separate one as it seems so similar.