Multichannel firmware loopback connection not working

[m-korber]

I have an issue with multichannel firmware: https://github.com/marckleinebudde/candleLight_fw/commits/multichannel/
I'm using it on a CandleLightFD adapter (connected to a Raspberry Pi 5) but it might also appear on other multichannel adapters.

The two buses are working fine (at low and high speed) when connected individually to a second CAN converter.
However, when making a loopback connection between CAN0 and CAN1 on the same CandleLightFD adapter, I receive lots of ERRORFRAMEs, e.g.

TX from CAN0 to CAN1:

[...]
(2025-04-22 05:24:36.892205)  can1  RX - -  023   [8]  FF 01 00 00 00 00 00 23
 (2025-04-22 05:24:36.894837)  can0  RX - -  20000020   [8]  00 00 00 00 00 00 84 00   ERRORFRAME
        no-acknowledgement-on-tx
        error-counter-tx-rx{{132}{0}}
[...]

TX from CAN1 to CAN0:

[...]
(2025-04-22 05:20:47.505364)  can1  RX - -  20000020   [8]  00 00 00 00 00 00 80 00   ERRORFRAME
        no-acknowledgement-on-tx
        error-counter-tx-rx{{128}{0}}
[...]

Test has been performed with assembled termination resistors on both ends and low speed (50kBit/s).

Can someone confirm that this use-case should basically work? Any idea what to try?

Thanks!