I have noticed the proble with the conda-forge install of jupyterhub+jupyterlab+ipykernel+ipyflow (large but fairly standard install). After installing of ipyflow some (not all!) notebooks stop responding to Ctrl+Enter and "run cell" buttons. This is also for notebooks running ipykernel! Just installing ipyflow triggers this behaviour. I have verified it also on standalone conda-forge install (just jl+ipyk+ipyflow). This is really unfortunate. I had to remove ipyflow from the install due to the fact that it affects non-users. I have no clue what is the reason and real trigger but I can run some experiments if necessary.