This has been happening for a while, and I've been wondering why. I couldn't find anything else related to this, so I thought I'd ask. And yes, I have been connected to the internet while this happens.
Each time I enter developer mode in MS Edge, it says it's disconnected, however, upon exiting and refreshing the page it loads normally. Sometimes, this doesn't happen when just entering Dev Mode, but upon resizing the window (see image - "Dimensions: Responsive"). Doesn't seem to happen on Brave or Chrome, just Edge.
Things I've tried (but to no avail):
Well, based on the image you provided, I did some tests and I found that the reason might be this:
By default, it chooses the option: No throttling
And then you may have accidentally changed its option to: Offline
After this, when you close and reopen devtools, you will see the image in your post,like this:
So you just need to modify it to the default option No throttling
to fix the issue.