1. If one (or more) parallel stage is skipped due to "when" condition in declarative pipeline, Blue Ocean UI does not show up running steps inside active stages until all steps in all active stages are finished.
2. In such case If one of steps is "input" step, there is no option to "Proceed" or "Abort" using Blue Ocean UI since no steps are shown up. It can be done only using regular UI or console output.
3. If all stages are active, steps are shown up, but after some time it is impossible to switch between output of "Stage A" to "Stage B" and see steps of "Stage B" until all steps in "Stage A" are finished. Refreshing page in browser (F5) allows switching between stages for some time.