Yeah i also only recently discovered this when i added a 10G adapter on my thunderbolt 2 chain that also had a mini monitor and a small raid. Individualy all good but when network was used raid slowed and when mini mon was used net was slow down etc etc etc. Turned out my 2 separate TB ports where on the same internal TB bus so....
Needed to reshuffle the lot and moved RAID off TB to just SATA drives with softraid as no more free PCIE slots for other types of solutions
But its all sort of working now with some minor limitations.
Beatstep & APC-40 Resolve Edition Controllers https://posttools.tachyon-consulting.com
Test Rig : 2xXeon (24c) | UNRAID KVM OSX VM's | 128GB | 5700XT | 40Gbe
Prod Rig : i9-7940X (14c) | OSX 10.15 | 64GB | 2xVega 56 | 40Gbe | Tb3 | V:Eizo | A:5.1RME