Twisted pairs are used for differential signals (balanced) hence a good to a very good electromagnetic coupling between the wires. Lets have following scenario: one twisted pair, 1st wire is MISO and 2nd wire is MOSI. MISO is high and MOSI is switching from high to low. Due of good electromagnetic couple between those two wires MISO will "see" this transition. Now, depending on how strong the "attack" is MISO can detected a bit even when is not there.
You have following options:
1. Use twisted pairs but check before hand what combinations of wires will gave you the best result
2. Use it only at low speed and short distances: <100K and <2m (you must experiment and check).
3. Untwist the wires and use 4 wires from two pairs
4. Use a single wire from each twisted pair for each signal and remained wire used it as ground
5. Use a complete different cable:
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For longer cables you take in account the EMI and EMC issues (ferrite core on cable, ESD protection, etc) especially when you want to go at higher speeds.
For more info:
https://www.maximintegrated.com/en/design/technical-documents/tutorials/7/763.html
My suggestion will be to use something else like RS485 or CAN or CAN-FD to communicate between boards, then you can take full advantage of twisted pairs. With power over line second board can be remotely powered but increase design complexity.
All the best and good luck!