Of course, the Israelis know there is an underground tunnel, they built the hospital!
There was an article from an Israeli newspaper about this that showed up on my feed, but went grail. Fortunately, it's mentioned in the wikipedia article since I am feeling too lazy to hunt the original article down.
Anyway, the hospital underwent a major Israeli renovation and expansion in the 1980s. Israeli architects Gershon Tzapor and Benjamin Edelson in their Tel-Aviv office handled the project, both were well experienced in the construction of high standard hospitals. The architects also designed and built a large array of underground infrastructure, which was what the IDF later pointed to as part of the underground Hamas command in both the 2014 and the current Israel-Hamas war. In particular, in 1983, the Israelis built "a secure underground operating room and tunnel network" beneath Building 2 of the hospital.
I would also add that the "guardian list" shown by the IDF is a calendar, not a real rota of terrorists. Toss in that the IDF spokeman reads the Arabic from left to right, instead of right to left. You'd think someone who speaks Hebrew would do it right.
Unless Hamas uses weekdays as codenames for its fighters.
Remember the USS Liberty? Israel wants you to believe it was an "accident". And don't forget those "weapons of mass destruction".
Has anyone found them yet?