This is because when the engine is on the flywheel is spinning and your clutch is not fully releasing the friction plate from the flywheel so there is pressure on it so it is hard to engage. When the engine is off, this is not happening so the shifter drops right in.
I suspect you have an issue in the slave cylinder or throwout bearing which is causing the clutch not to release.
I attached a number of guides that will cover this issue a couple different times.
I suspect we are going to have to replace the clutch and when you are there, we do the slave cylinder, bearings and then bleed the system.
Let me know what questions you have after you review this material. Thanks
Friday, May 22nd, 2020 AT 6:51 PM