It’s a known issue and as far as I know it’s not fixed yet. There is a workaround though. This is my file paths and it might differ on your setup. Hope it helps.
# edit .treeinfo file
/var/lib/pulp/published/yum/https/repos/Default_Organization/Library/custom/CentOS/centos-8_2-baseos-x86_64/.treeinfo
# at bottom of file change from:
[variant-AppStream]
id = AppStream
name = AppStream
packages = ../../../AppStream/x86_64/os/Packages
repository = ../../../AppStream/x86_64/os/
type = variant
uid = AppStream
# Change to
[variant-AppStream]
id = AppStream
name = AppStream
packages = ../AppStream/x86_64/os/Packages
repository = ../AppStream/x86_64/os/
type = variant
uid = AppStream