The new pause button you can use to pause the Cycles viewport render remembers its state across saves and render mode switches.
If you’re in Cycles and you pause the viewport render, then switch to, for example, solid mode, then back to rendered mode, you get a blank viewport and the render is still paused - worse, the render status doesn’t say ‘rendering paused’ any more, it stays stuck on ‘inititalizing’. This persists even across saves, so once you’ve completely forgotton you ever paused the render, it stays paused. The only indication that you’re paused is the highlighted pause button in the corner, but that’s easily misread as the button being highlighted because you’re currently rendering.
In my view the best behaviour would be to reset this as soon as you switch to another mode, or re-open the file. The next best behaviour would be for the message to say ‘rendering paused’ as it usually does.