The troll assembly is tough to access. I had to replace the right troll head as the back of the head has 2 holes, the lower of those 2 holes is awfully close to the bottom edge and the plastic margin is thin enough to break on troll hits. It is possible that your troll is not secure as well as what was suggested in the prior post. To access the troll and take a look is the hardest part. Here is what I do:

1) Underneath the playfield, wedge something between the plunger bottom and the bottom of the troll assembly bracket to put the troll in an up position have it sticking out above the playfield.
2) Wedge a post rubber between the troll trap door and the top of the troll head to give some clearance to look at it. DO NOT REMOVE THE TRAP DOOR FROM THE TROLL ASSEMBLY. It is too hard to re-assemble.

Actually replacing the troll head can be done without taking the whole assembly out, via unscrewing the 4 screws underneath the playfield. However, for replacing the switches maybe you need to pull the whole troll assembly up through the playfield. There has been good advice on other threads on how to do that check out the MMR dedicated thread or LTG here's advice..

One good piece of advice I was given here is that for Troll work, get yourself an ignition wrench. I bought a range of 3 from Home Depot or Lowes I forget which one. The wrenches were 1/4, 5/16 and 11/32 I think. The 11/32 is the one that fits I believe but I am going by memory. Check out the MMR dedicated thread I explained everything there I believe when I did it a couple of months ago.

Same thing happened to me when my right troll was loose as I explained earlier here. Your troll is loose.