apk update -- WARNING: opening /repo: No such file or directory for existing repo

I'm trying to collect apk packages to local repo to install them later. But apk update says that this repo directory does not exists (what is not true). It does not depend on actual location and is very strange Run alpine:

docker run -it --rm alpine:latest sh

Create repo inside and try to use it:

/ # mkdir /repo
/ # apk fetch --recursive -o /repo screen
WARNING: opening from cache https://dl-cdn.alpinelinux.org/alpine/v3.21/main : No such file or directory
WARNING: opening from cache https://dl-cdn.alpinelinux.org/alpine/v3.21/community : No such file or directory
screen: unable to select package (or its dependencies)
/ # apk update
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/main/x86_64/APKINDEX.tar.gz 
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/community/x86_64/APKINDEX.tar.gz 
v3.21.3-357-g39d49089a10 [https://dl-cdn.alpinelinux.org/alpine/v3.21/main] 
v3.21.3-358-g5686bc96b73 [https://dl-cdn.alpinelinux.org/alpine/v3.21/community] 
OK: 25396 distinct packages available
/ # apk fetch --recursive -o /repo screen
Downloading libncursesw-6.5_p20241006-r3
Downloading linux-pam-1.6.1-r1
Downloading musl-1.2.5-r9
Downloading ncurses-terminfo-base-6.5_p20241006-r3
Downloading screen-5.0.0-r0
Downloading skalibs-libs-2.14.3.0-r0
Downloading utmps-libs-0.1.2.3-r2
/ # cd repo
/repo # ls -lah
total 1M     
drwxr-xr-x    2 root     root        4.0K Apr 21 17:54 .
drwxr-xr-x    1 root     root          63 Apr 21 17:53 ..
-rw-r--r--    1 root     root      154.9K Nov 11 17:11 libncursesw-6.5_p20241006-r3.apk
-rw-r--r--    1 root     root      191.0K Oct 30 12:34 linux-pam-1.6.1-r1.apk
-rw-r--r--    1 root     root      401.7K Feb 13 17:58 musl-1.2.5-r9.apk
-rw-r--r--    1 root     root       20.8K Nov 11 17:11 ncurses-terminfo-base-6.5_p20241006-r3.apk
-rw-r--r--    1 root     root      431.5K Oct 30 12:35 screen-5.0.0-r0.apk
-rw-r--r--    1 root     root       76.2K Oct 30 12:35 skalibs-libs-2.14.3.0-r0.apk
-rw-r--r--    1 root     root        4.9K Oct 30 12:35 utmps-libs-0.1.2.3-r2.apk
/repo # apk index -vU -o APKINDEX.tar.gz *.apk
Index has 0 packages (of which 7 are new)
/repo # apk update
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/main/x86_64/APKINDEX.tar.gz 
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/community/x86_64/APKINDEX.tar.gz 
v3.21.3-357-g39d49089a10 [https://dl-cdn.alpinelinux.org/alpine/v3.21/main] 
v3.21.3-358-g5686bc96b73 [https://dl-cdn.alpinelinux.org/alpine/v3.21/community] 
OK: 25396 distinct packages available
/repo # echo "/repo" >> /etc/apk/repositories
/repo # apk update
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/main/x86_64/APKINDEX.tar.gz 
fetch https://dl-cdn.alpinelinux.org/alpine/v3.21/community/x86_64/APKINDEX.tar.gz 
WARNING: opening /repo: No such file or directory
v3.21.3-357-g39d49089a10 [https://dl-cdn.alpinelinux.org/alpine/v3.21/main] 
v3.21.3-358-g5686bc96b73 [https://dl-cdn.alpinelinux.org/alpine/v3.21/community] 
OK: 25396 distinct packages available