So you arrive at the Uncrossable Jungle only to find out, that only two of the three locks on the very first gate are being opened by turning the staff with the old fart? This seems to be a PC-exclusive glitch, but fortunately, there is a way to fix this.

After trying to open the gate (And obviously failing), head back to the starting point to leave the area towards the City Docks.

After re-arriving there, immediately re-enter the jungle. The gate is now openable normally.

Why? I have no idea. The only downside to this is that you will need to rewatch that unskippable cutscene, but ah well. At least you're game isn't ruined, right?