I am afraid we do not offer official support for dev insider builds so you may encounter issues like this.  We will note the issues but cannot offer any promises that everything will work or give a timeframe on any possible fixes.

Those Windows builds are changing week to week so features may break and get fixed and the builds are not intended for consumer use.

This bug seems to only be present when the taskbar is set to small. When it is sized to either medium or large it actually functions just fine. I have also seen mild texture discoloring, if you resize the task bar up then back down it should fix the texture.

I am seeing that as well.

I am not sure if there is yet an official strategy on how Beta builds will be developed for. But I do imagine there will be a much higher probability that the Beta channel gets fixed a lot sooner then whatever is released on the DEV channel so I would still switch to the Beta channel in the event you are on the DEV channel

Just wanted to get these issue out there. I'll gladly go into more details if anyone is interested. Not asking for support as seems to be the assumption by some. I'm trying to help identify the issues here.

I'm having several problems that popped-up new with this Insider version as well. Start11 taskbar flashing and not recognizing any mouse clicks, right nor left buttons. The same problem I had with coming out of sleep mode, or even screen saver (which I have set to blank the screen) the Start11 taskbar drops down as if the previous location at the top of the screen is now reserved for something else, but now it also comes back covering only 3/4 of the horizontal real estate. As if it is painting in 16x9 instead of 21x9 aspect ratio of my main monitor.