What's the basis for preparations to imminent Russian invasion into Ukraine?

A follow-up to previously closed question.

As of Feb 13th, there's still no Russian invasion into Ukraine, however, some countries are retracting their air traffic to Ukraine and even de-leasing airplanes of Ukrainian airlines.

What's the informational basis that the relevant parties base their actions on? What facts would lead to such severe actions?

I can see two options there:

• The actions are mostly triggered by each other in cascading fashion (one party decides to play safe and that fact is used as a signal for other parties to implement more severe restrictions and so on) - a bank run situation (a country C will stop air traffic/evacuate its citizens since countries A and B already did either of those)
• These actions are based on input of facts about Russian invasion which are independent of cascading reactions and would exist/be sufficiently compelling even in the absence of those reactions (a country C will stop air traffic/evacuate its citizens even in the absence of any actions from A and B)

Can you reason for one of these or maybe there's a third option?