1. I just went back and did a fresh code compare and discovered I somewhat changed the way it handles the taskbar button. I've reinstated the old way so we'll see how that goes.

2. I'll test that scenario tomorrow.

Thanks Glenn, I'll keep an eye out for the next release with updated code!

So let's be very explicit. 

You have no monitor entries in the config.

The external monitor is the primary monitor.

Start DTI, it displays on the primary monitor.

External monitor is disconnected.

The primary monitor reverts to the laptop.

DTI is no longer displaying on the primary monitor.

Reconnect external monitor.

Primary monitor switches to external monitor.

DTI is still not showing.

Does task manager suggest it has stopped responding?

Are there any error entries in the log?

Have you tried the display-change option?

Morning Glenn,

Yes, exactly the steps and facts you listed.
This is with display-change=1. 
The task manager indicates DTI is still happily running, and I didn't find anything in the log - although I may not know what to look for in honesty!

Like I say, the monitor is a minor bug that can be lived with as it works in most scenarios! I'm more keep to test for a fix of DTI appearing on the taskbar 😀 

Thanks in advance as always!

@marts4 I've tried every possible combination and can't reproduce it. There is something unique about your hardware arrangement. It is displaying itself somewhere other than on a visible monitor. You can try adding UI to the log-level and see what it reports as you move between primary monitors. Don't leave it on though, it makes for a big log file.

I also receive this intermittently on various physical desktops and VMs.

Morning Glenn,

Apologies for the delay, a busy week!

I've just re-tested with v3.19.5, and UI logging.
Though, I couldn't reproduce the screen switching issue - I'm pleased to report.
I set the monitors to extended (larger USB-C dock/ monitor being the primary), unplugging and replugging the USB-C as before.
I only observed DTI was perfect re-connecting and switching to the larger USB-C primary display, but a little buggy switching to the 14" laptop as primary after unplugging. Still works perfectly well though, just took a few seconds to resize 3 or 4 times before settling down. I've attached the UI log for this anyway, if it's of interest. Although, I'd be perfectly happy with this in honesty. IMHO, I think it's just the DTI handling of the 14" scaling calculations, and the end result is always correct now anway!

In regards to the greater taskbar issue, it seems v3.19.5 didn't remove DTI displaying on the taskbar.
It also introduces another bug, where DTI overlays te taskbar and date/ time tray area.
I think this is still the case only where DTI loads before the taskbar does, I launch DTI via scheduled task at user login with 5 secs wait. 
I also observerd where the taskbar appeared to load before DTI, everything was displayed exactly correct!
That all said, I would say v3.19.5 with the current 5 secs wait, is more reliable (at not displaying on the taskbar) than some of the recent versions prior. Where the new code of prior versions displayed DTI on the taskbar 9/10 logins, I'd say this version is akin to 1/10 or 2/10 logins.

This may be unrelated, but we found on v3.19.5, the desktop sometimes appeared black (lost wallpaper etc). The wallpaper was there, but then goes black for around 10 secs before coming back. Like I said, it may be completely unrelated, but it's strange DTI refreshes/ reloads at the same time the wallpapre re-appears. Again, only around 1/10 logins (not always the same logins as taskbar), so nothing major.

Again, thanks in advance - it truely is a great programme! 😀 
I'm also hoping to begin testing DTI on our VDI enviroment soon!

@marts4 Thanks for the report. That tells me DTI is probably jumping the gun in a few situations where the desktop is in transition. I'm going to roll back a few changes I made in recent builds that try to shorten the reaction time to such transitions.  It's better it waits for Windows to finish doing whatever it's doing before DTI reacts. In addition I'll add a call to it's "reaction" code to make sure the taskbar button has not snuck back.

The black happens when it gets interrupted during a display refresh. At some critical point it suddenly loses cpu to some other higher priority windows process. It's annoying but not something to worry about, it will continue when Windows gives it cpu time.

I've studied the log file and I'm of the opinion that DTI is reacting way too early to the WM_DisplayChange message while other messages are still rolling in.  The time between when that message arrives and when DTI reacts is the number I've been tinkering with. I'll set it back to where it was several versions ago but I'll also add it as an option in the ini so it can be adjusted according to the environment.

Thanks Glenn, much appreciated! I'll be happy to make some tests once you have it released 😀 

I'm also pleased to say, I did deploy v3.19.5 company-wide as it was certainly more reliable than the version we had been pushing. So far, reports with this version showing on the taskbar or black screenining have been very minimal. Perhaps my 1/10 estimate should be more like 1/30 or 1/40 in real world findings. We did observe a higher number of instances where DTI didn't complete it's load/ refresh, likely relates to the CPU you mentioned. For example (in order of appearance and ini config order), we have first/ top-right company logo (always loads), we have hyperlinks next/ top of the bottom-right area (loads 99% of the time), lastly we have also very bottom-right hostname, username, and uptime (these seem to be missing mabe 5% of loads). Presume the CPU is grabbed part way though or something like that, and it absolutely always sorts itself out at the next refresh.

I hope this helps you in tracing this down.

I've closed/killed DTI and relaunched it from the EXE. It will work properly with nothing on the taskbar for a few hours, then it just shows up on the taskbar. No other intervention done.

I can reproduce this every time.

I'm still running 3.19.3.4825

Another side oddity is sometimes we'll see 2 instances of DTI running. No idea where the 2nd launch is spawning from, but it's not happening to everybody.