I was trying to place one small station right next to another one and it turned red showing that I wasn’t allowed. Do you not allow some even though they physically fit? Or is this a bug? If it is bug let me know and I will try them again to let you know which ones specifically.
Its a bug, it should only happen if those two cannot connect (ie you have missed out a step), but I suspect there is some bad data with certain slots preventing the code from working properly, definitely something I need to fix. if you know the specifics of which ones it happens to, it would be very helpful. I encounter them rarely but have been too focused on other stuff to make a list 
The problem is with the order of the front/rear arch in the menu. For all stations except arch the components are in the order that they need to be installed. But Rear Arch comes before Front Arch in the menu but when placing them this way the line won’t keep moving. But before I discovered that I tried to place Fit Vent next to Fit Front Arch and that is when it showed up red. Not being able to put them next to each other is correct.
aha cool. we fixed that arch thing in todays patch actually.
Just noticed one that is a bug. I am trying to place Fit Windscreen next to a conveyor. The next station after is Fit Electronics. The Fit Windscreen turns red seeming to say I can’t put it there. I does however let me place it.
Looking more closely at the second one I see now that the conveyor is flowing in the wrong direction.