Why is there zip tape at the bottom of the wall? Does the zip overlap the concrete by at least an inch? No roof overhangs, lack of a drip edge, and lack of support for the edges of the shingles may not be causing the problem, but is not a good idea.

Incorrectly installed zip system, and incorrectly roofed. None of the parts are integrated correctly. Plus it appears that the ground does not slope away from the building correctly.

I would think siding properly installed on the outside of the walls and roof overhangs and the space required between the bottom of the siding and finished grade would help eliminate the problem.

Zip tape won't adhere to concrete so base flashing or "Liquid Flash" should be used.

Clearance from wood sheathing to grade less than 6" encourages splashback and so does an eave drip too close to the wall.

Was a roller used on the tape?

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Have you noticed a pack of large dogs roaming the neighborhood that drink a lot of water and would have access to the inside of the structure in question??

(Hey, you have to explore all the possibilities)

Figure out the path of water. More photos of the roof 4 sides. Gable end looks short. Are there openings on the roof, walls or gable end? The flashing above the window - is it tape or loose? Was the door flashed?

Was there a ground flood? This isn't a submarine.

The home is not completely "weathered in" and is not ready for electrical or HVAC. After you correct the water intrusion you need to complete the exterior wall weather proofing

" Im in the process of building a Tiny House in my backyard "

Are you converting something, some of the framing looks new, some is showing some gray like it is not fresh and the roof shingles look older?

Too bad Huber's Installation Manual wasn't consulted before the work began. Good reminder for me!