I create new file [not my original]. But here are it reproduce on my PC. If you PC more powerfull - you will don't see it. So please just increase subdivisions on the object [when you fill the same slowing down as in the video]
Here is how it looks like: https://mega.nz/#!cLBQHIIa!UYt3WhuyBA0twL6P5J29fC5jnK7X97zjwRmbRM2c5m4
Btw, I checked it whith pressing 'Enter' key - and it works fine. But with mouse - not.

STEPS: open file. Press G to move. Press Z to lock by Z axis. Move precisely to the ~zero position by mouse. Then press mouse to finish action and then move mouse upside without waiting long time.

I can't reproduce this on my end, the file is even slower for me than in you video.

However, in you video you can see that the mouse cursor does not change right away when you left click but lingers around. On my end it changes quite fast after I left click (even if the scene is many times slower for me than in your video) so I can't get it to change position after I have clicked.

@Ray Molenkamp (LazyDodo) @William Reynish (billreynish) can you guys see if this happens for you on Windows/Mac too?

This sounds like a similar issue to this bug: https://developer.blender.org/T63699

@Sebastian Parborg (zeddb) - yeap

In T63185#652800, @Ruslan (rs2128) wrote:

fFILE.blend4 MBDownload

I create new file [not my original]. But here are it reproduce on my PC. If you PC more powerfull - you will don't see it. So please just increase subdivisions on the object [when you fill the same slowing down as in the video]
Here is how it looks like: https://mega.nz/#!cLBQHIIa!UYt3WhuyBA0twL6P5J29fC5jnK7X97zjwRmbRM2c5m4
Btw, I checked it whith pressing 'Enter' key - and it works fine. But with mouse - not.

STEPS: open file. Press G to move. Press Z to lock by Z axis. Move precisely to the ~zero position by mouse. Then press mouse to finish action and then move mouse upside without waiting long time.

I tested this scene, but I can't reproduce this issue. Moving the polygon is slow, but there is no buggy behavior as per described above.

System Information
Operating system: Windows-10-10.0.17763-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 432.00

Blender Version
Broken: version: 2.82 (sub 6), branch: master, commit date: 2019-12-23 08:34, hash: rB708045eb40b9

🤔 I think @Daniel Bystedt (dbystedt), you know better what to do whith this task for further(if it will not reproduce by anyone)...
I've checked it just right now with (version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: rB26bd5ebd42e3) and it still reproduce.
Then I've checked it on last fresh (version: 2.82 (sub 6), branch: master, commit date: 2019-12-23 08:34, hash: rB708045eb40b9 ) and it still reproduce.

Each time when I put stylus(alanog of press left buton on mouse) to ending action and then move it away (it stick to my movement until curson not changed his icon to crosshair from (G)move-icon)
It seems like because it too heavy and processing-calculate movement too long, it can't fast change to ending mode. And it still stick to the stylus movement until calculation will be finished. Maybe key of the issue in that I'm not use mouse? (just wacom-tablet) Try with tablet, maybe it helps to find reason 🙄

Sorry to hear you still have the issue. I can't reproduce the same thing on my computer.
I just want to confirm that I'm also using a tablet (wacom intous 5 touch)

Cannot confirm that on linux.

Don't think we can do much here really? This is likely some problem where event handler gets wrong coordinates from the OS event system, due to heavy load.

This seemed to me like after click event was received, OS was polled for position or we wait for another position event. I wouldn't assume, that problem or limitation is on OS side, many apps can handle this.
But I am not familiar with our event system at all...