Nexperia F/F problem

The obvious question is did you try reversing one of the parts? I've never known lettering to be rigorous for chip orientation. How about photos of the top and bottom of the part?

Flipping it would put GND where VCC is and vice versa, dead short thru the protection diodes. current limit on my supply was set at 50mA it didn't engage.

Well I can try it but I didn't order too many of these for testing. I should probably always get batches of 10 or 20 I guess.

I'm having trouble getting a good pic of the lettering even under high magnification, there's something there though other than the darker "bar."

Top row looks like "O85" maybe? D85?

Bottom row is definitely "94Z"

Black bar to the left running the width of the chip, about 1/5th its total area

Bottom of chip is featureless

Try ohming the Vcc/Gnd pins. Does that tell you anything?

They don't have reference drawings on the datasheet?

Floating-inputs can make currents that high. Whether an open input will create such a current is a function of what voltage it floats too, and is not predictable. When struggling with soldering, an apparently-soldered connection may in fact be open underneath. A floating input causing internal rail-rail current can certainly cause logic malfunction.

Yeah, it's weird, the US8 parts were the pisser to get mounted, but once I inspected carefully that everything was making contact, no bridges, and continuity-ed all the pins to check out OK they work fine.

The SOP parts seemed superficially a lot easier to hand-mount to the surfboards and seemed to check out as well but something's going wrong.

I'll consider it user error for now and try mounting some more and see what happens. It's curious/irritating the parts have no "dot" indicator as the datasheet says they should, though.

I've had luck wetting a cotton swab with a small amount of alcohol and swipe across the top. Helps make the pin 1 dot easier to see.

Go to the website and get document SOT505-1_518, which shows component orientation in the tape. For tssop8 it says, with the sprocket holes up, pin 1 is on the upper left top corner. That's always the best way to determine orientation.

So did you ever resolve your problem?

Away from home for the weekend, got another pack of parts and "surfboards" from another mfgr coming in, standby :)

Might the flops be counterfeits? Did they come from an authorized distributor?

Seems the least likely possibility as they came from Mouser, but possible.

Datasheet says the package is supposed to have a dot indicator but there isn't which is at the very least, annoying.

I'm trying a different set of "surfboards" from Adafruit, too, as there's a chance the no-name Amazon boards are bad: