Combination Chests Can Fail?

encountered a chest, and tried 1,2,3 ,all red
then tried 4,5,6 ,5 and 6 are yellow while the others is red
then tried 7,8,9, 8 is yellow while the others are red
then the last attempt came,with a tangle of 2 alternatives---end up with 5,6,8 or 8,6,5?
thus trying 5,6,8?then locked

Yes... that's what chests do
4 incorrect guesses lock the chest

Not so efficient strategy.

There is an advance strategy that will get you to 98% success by altering the third attempt according to what you get in the first two.

Just some advice:
Your third try should have been 7 8 5
If 7&8 are red, you also know if 9 is a correct number.
Plus it gives info over the position of number 5

123 all red
456 4 is red and 5,6 are yellow
Your third attempt should be
568 and clue should be enough to guess right cause in 3rd attempt there's a chance you'll get green ones or twos.

but if 5 is right ,then 5 is for certain(third), 6 can be first and second ;if 7 and 8 are wrong,9 can also be first and second.
so it seems there always be a little chance to fail,but yours seems make that chance less

yours also be great although a tangle with 7 or 9 may come

Just walk away and a new chest will spawn instead of guessing.

Well I thought so. I got teleported while mid combo chest I couldnt finish and a new one spawned shortly after. However the old one also spawned about an hour later so likely just a coincidence.