The lane change switches are listed in the switch matrix as "flipper EOS" - they don't mean the high powered end of stroke switches, there is a secondary switch on each flipper used for entering your initials if you get a high score. Make sure the outer low power switches on the stacks are not shorting to the high voltage end of stroke they should be isolated either with fishpaper insulator or a plastic piece.

Switch level test will never show intermittent/quick switches, it shows every switch currently closed in a loop. Switch edges would detect switches but it's really quick, and if it truly is 2 switch at the same exact time (relatively speaking) it will only show one.

There are some RC networks on system 11 boards in the switch matrix that sometimes go bad, worth a look. Seek out posts from DumbAss and GRUMPY they talk about this a bit.

They must be in the cabinet then.

The switches themselves do not have caps on system 11 and they can't as first activation causes them to repeat.

There are caps in the return section which can be problematic... Top section of the schematic page he posted. Based on what's been going on so far that's where I think the OP should look next.

Take all the switch input plugs off see if flippers activate the switches then you know it's the board.

AFAIK those caps are in the circuit to limit false positives from the wiring acting as an antenna. Since it's still doing the phantom switches with the connectors off, I'd temporarily just remove them and test. They might test good but they might also be the source of the phantom signal.