When you have 2 images open, closing the one you are currently on will automatically place you back on the other. In recent versions of Krita Plus, this will cause the canvas to stop rendering entirely. This does not happen when closing a tab that you are not currently on. To reproduce: Open 2 new canvases, close the one you are currently on. To fix the bug if you have it: Open a new canvas, swap to your artwork, then close the new canvas. Alternatively if you have other tabs open, swapping to another tab and back will fix the canvas.
I don't see this happen with the 18 Jun 4.3.1-alpha (git f88a88) appimage or the 18 Jun 5.0.0-prealpha (git a98fccf) appimage. I can confirm it happens for the 19 Jun 4.3.0-prealpha-gaa9505a5a2 Windows portable zip package. It happens with OpenGL and with Angle rendering.
This was fixed shortly after posting, closing.