Minutes delay resistance change - Simulation mode and Erg mode

I’ve experienced this problem many times.
When I ride into Zwift in simulation mode, the hill resistance comes in late, like 2 or 3 minutes after I passed the hill. It comes when I’m on a flat part.
This is very annoying and I don’t know why it happens.
I’ve also experimented some power stuck during a workout session on Erg mode. Or minutes delay, like before…

Zwift is running on an iMac on MacOS 10.15, a Tacx Flux Smart connect by Bluetooth.

@Bastien_Marragou have you put your log file from those rides where you experience delayed resistance into www.zwiftalizer.com ? It may show BLE or ANT+ interference on those rides that could be causing the issue.

I checked the logs. It seems that the iMac (or the Zwift app on MacOS) cannot send grade information to the HT controllable by BLE. I got this error :

[9:44:01] [FTMS] SIM (1.4)
[9:44:01] BLE : bledevice - SendBLEResponseToGame received the following error for device Tacx Flux 58818 characteristic 2AD9 ERROR: Unknown error. Error Domain: CBErrorDomain=0
[9:44:01] BLE Mobile Response error 0 : Unknown error.

If I connect the HT controllable part through my ANT+ dongle, Zwift sends correctly the grade information (and the resistance is well updated) :

[9:59:53] FE-C SIM GRADE 0.013
[9:59:53] ANT : Transfer Completed.
[9:59:53] ANT : FET grade set successfully

All the other paired devices (Power source, Cadence, Heart Rate) work perfectly by BLE.

@Bastien_Marragou I have the same setup as you (mac and flux) and I am also experiencing this issue A LOT.

@Alec_Smith_USMES The only solution I’ve found is to connect the controllable part through an ANT+ dongle, and all the other sensors through Bluetooth. It seems that the Mac Bluetooth driver does not control the Flux correctly. My ANT+ dongle does it well. Note that the powermeter sensor should be connected by Bluetooth, better reads than ANT+.

+1, same here, same errors, same symptoms. Delay gets progressively worse during the length of a ride. On a recent 2h10m ride, the latency was almost 8m by the end. Emailed Zwift and Tacx for guidance and submitted logs. Any resolutions other than changing to an ANT+ connection?