Zephyr SPI 1 issue after migration from F746zg to F756zg

[STM32Fuser]

Hi all
I migrated from a Nucleo F746zg to a F756zg. Code and overlay is the same except that I west build against F756zg. Now SPI 1 is not working properly anymore. On the scope I can see that SPI communication starts (CS goes low, MOSI byte is sent, MISO byte is sent back) but the transfer does not finish. I ran the same but using SPI 3 this worked flawlessly. Don't know maybe an APB or FIFO issue?
Anyone an idea?

Sorry, I forgot to say that I tested this with a Zephyr RTOS firmware (which worked with the F746zg) and as well with a simple straight forward Board-to-Board HAL_SPI_TransmitReceive Ping Pong F756zg (SPI 1 master) <-> F746zg (slave). Besides I want to mention that the same Ping Pong with F756zg (SPI 3 master) <-> F746zg (slave) worked flawlessly.

[STM32Fuser]

We had 2 more new F756zg in our lab. I tested both with the same setup. One worked immediately. The other showed a way too low MOSI high level (~300mV) but a clear signal shape. I applied a slight pressure on the MCU and immediately the MOSI high level became about the expected 3.3V. Don't know if it was because of the mechanical pressure or an EMC effect. Anyway, I'm a bit concerned...

Update:
I thought due to the soldering I did when moving the 0Ω resistor from SB121 to SB122 there could be some solder residuals between SB121 which could badly influence SPI1. I measured the resistance between the to pads on all three boards and all show ~23MΩ to ~21MΩ (in left(+)-to-right(-) direction in regard to silkscreen text direction). I guess this is ok.