So to update, I strongly believe I sorted out the issue mentioned above, and yep, seemed to be a switch issue there within that moving lock mechanism,and I do believe I have the issue solved.
So, the issue appeared to be a failure for the first switch in that lock mechanism to activate/click when a ball was passing by. That switch arm sat rather shallow and I believe the ball was bypassing that switch more times than not and when the ball got to the end of the locking mechanism and registered the last switch in that mechanism (the switch by the captive ball), in the absence of registering the first switch, the machine would think that there is just a ball that is randomly in there and needs to be dumped. And that's what was happening.
Of course, typical for messing with those switch arms, the more I messed with it, seemed like the worse it got! Haha. Finally able to get it to where it started and opted to tack a double layer of thin super sticky 3M tape on top of that switch arm, thus making it more proud (leaving the smooth vinyl backing on top so that the top was smooth). With this maneuver, making that switch more proud, any ball passing by was guaranteed to register that switch.
So, after doing the above, started the game with the glass off, hit the captive ball to register the tomb opening, sent a ball up the left ramp, triggered via audio and LCD screen a "sarcophagus lock," gate opened up, ball fell through into the moving lock mechanism, registered the first switch and then the second switch by the captive ball, the shaker shook, the mechanism went down to its mid position, the ball remained locked, and ready for mummy mb. So, seems like that was the deal. Whew.....
Of note, ivestigating this problem, I see that the physical switch mechanism in question is screwed into a metal plate by 2 small hex screws (and even with that locking mechanism all the way down, is hard if not nearly impossible to get to without taking the entire mechanism apart and out), and thus there is no room for any physical adjustment/movement of that switch mechanism. The metal arm associated with that small switch is typical in size but overall rather short and thus there's not much play with adjusting that metal arm. True, I wish I could have just raised that physical switch higher, but as above, that was not a possibility. I also wish I could have been able to successfully bend that switch arm to make it more proud, but has above, the more I messed with bending it, the less reliable it got...However, this "added height" on top of the metal switch arm with the tape seems to have addressed and fixed the issue. Fortunately, this added tape to make that switch arm more proud is out of visual sight (as the smooth vinyl backing is bright ass red, haha), and since it seems to have fixed this issue durably, I'm going to leave it as it is without messing with it further. So issue solved! Whew!! That said, if anyone has any other sage advice for what they did to make switch arms more proud outside of what I opted to do, I am always up for learning new tricks.