I think I've found something. I've looked into APKINDEX before the package is cached and after. ProGet is definetelly doing something to it.

I thing, that after caching package ProGet wrongly calculate C filed inside APKINDEX file (which is file checksum according to https://wiki.alpinelinux.org/wiki/Apk_spec).

Here is an example:

C:Q1UIflJfipsQ/A/h2DPh9PCYwROC8=
P:musl-dev
V:1.2.3-r5
A:x86_64
S:3225228
I:10346496
T:the musl c library (libc) implementation (development files)
U:https://musl.libc.org/
L:MIT
o:musl
m:Timo Teräs <timo.teras@iki.fi>
t:1684510151
c:b12380f8608f8cdd44347db413e8937ac4a5565b
D:musl=1.2.3-r5

• Before package was cached (no single download from feed):
  C: Q1UIflJfipsQ/A/h2DPh9PCYwROC8=

• Original value from official Alpine repo (which matches C returned by ProGet):
  C: Q1UIflJfipsQ/A/h2DPh9PCYwROC8=

• After package was cached (downloaded from feed):
  C:y3bwudQn8ZsMwZJVfU44wZ5WQFw=

As you can see, the checksum is being changed even the package itself is still exact the same file. This is definitely a bug.

I have exact same issue, I can replicate it every single time. I'm running Version 2024.3 (Build 4)

Scenario:

1. I've created two separate feeds, one for community and one for main packages:
   

2. Each of the feeds has one assigned connector, to corresponding repository. No issues there:
   
   

3. When i use feed for the first time (cache is empty), everything is working smoothly. But the second time, the cache is filled I'm starting getting error after using apk add on every package, that is already in the cache (was downloaded before). When I try do add new package which is not present in the cache, it will also work for the first time and only.

4. As the original author mentioned, when i manually clear the cache, I can again download packages but only once. After the cache contains the package, it will no longer work.

5. The apk update works every time without any error, no matter what.

6. Those are the error messages that I'm getting when trying to download package cached already by ProGet. I'm using ProGet while building docker images: