[SalesForce] Why Lightning Experience is freezing (crash, hang, become unresponsive) after reload via F5

While I'm developing Lightning Components I usually have this workflow:

• First I change my code
• Then I save it
• Finally I reload LEX to get the newest version of the component rendered via F5 to see and debug the results.

This is my usual development cycle.

But also when I'm working in LEX as user, I very often use F5 to reload everything. This I do unrelated from development, just to ensure that I see the most recent data.

Starting with Winter 18 I noticed a very odd behavior in at least two different flavors:

a) Regular freeze

Every second time I reload LEX via F5, it get stuck. It's freezing completely and the page becomes unresponsive.

b) Random freezings

Just using LEX (while development or just as normal user) and refreshing with F5 from time to time randomly the same freezing is happening.

In both cases a+b: there is only the release icon visible at that time:

Some time later a Page Unresponsive popup appears:

With Summer 17 this never happened. I cleared the browser cache, uninstalled all browser extensions, installed even different versions of Chrome, but none of this helped.

What is going on here?

At the network tab the freezing happen very early while loading one.app

Update

At least for scenario a) described above I found the reason – see it in the answer below. But this is not all: still b) is happening from time to time but it is rare enough to prevent me for debugging it to nail it down.

Also my colleagues and others here are reporting similar effects. It is happening irregularly. And it's happening on standard pages without any custom components, too. So in my opinion there is a serious bug in W18. Possibly multiple things can cause that – but it's nearly impossible for us to investigate that deeper.

Please feel free to add your scenarios (in the question, in comments or as answers if you solved such freezings).