Mystery flat - latex tube

Was out riding earlier and using a bike with Victoria latex tubes and GP5000. Pre ride check and all looked good - inflated rear to 95 and front to 90. Went out for my rider and 3/4 way through felt like i was on rear suspension. Topped up the air since there was no evidence of a flat and went on - you used it tire went low again and I changed out the tube and limped home.
Inspected the tube and cannot find a leak anywhere. Filled it up enough to give it some shape and had to jet out the door but as far as I can tell there is no leak based on a quick fill and listen.
Anyone else experience this?

Not on latex, but I’ve had it happen on Butyl once. Best way to find the leak (because there probably is one) is to fill the tube and submerge it in water, and watch for the bubbles. I took that butyl tube that I couldn’t find the leak or cause and sure enough, there was a pinhole, and I was able to patch it. You probably hit a thorn or something similar and it may have removed itself but had already done the damage to the latex tube. As you know, it doesn’t take much with latex…

That’d be my guess too - but in my quick look over after adding a fairy amount of air there zero sound of a leak. Ill have to dig in further when I return home - thanks for the reply.

I have had this twice with different tyres and different inner tubes – with the same wheels, though.
I did set up the tyre properly, pumped it up, and after a day or so, the tyre is soft. For the first time, it even took couple of days to get soft.

I expect this to be because of the tyre does not initially sit properly in the wheel. My wheels are tubeless ready so it may take some effort to make the tyre sit. However, I expect that sometimes it takes some time before the tyre sits in the bead. When the tyre gets to its place, it gives the inner tube a bit more room. This decreases the pressure in the tube and the tyre gets soft.

When I switched to Stans tape the mystery flats were less frequent. So for me, it probably had something to do with the spoke hole/tape situation.

With that said, Ive given up on latex. Even post Stans tape the tubes are just too finicky and inconsistent to worry about it. Where they are sealed together seems to be another area where you never know. You know?

Submerged the tube and not able to find a single bubble. Weird.

Valve core issue? Sometimes if you don’t seat the nut air will leak out. Not a latex thing per se but, something to check at higher pressure…

That is weird. Bad valve like Landis suggested is about my only other thought, but some other smarter guys might know more.

Patched my neighbors tube a month ago, I’ve got a pool and a lot of experience finding leaks. Had to spend 5 or 10 minutes finding the small leak. Unusual but it can happen.

I think it is loose core. I’d remove the core, wet the seal lightly and re-seat reasonably tightly.
10psi when inflated outside tyre may not leak, but 90psi sure will.

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Thanks for all the suggestions - removed the valve core and reinstalled it with no luck - thanks to all for the help though - much appreciated.