OpenBSD: group access on NFS share?

I'm exporting a filesystem from Ubuntu 22.04.5 via /etc/exports:

/mnt/exportTest/ 192.168.129.8(rw,async,no_root_squash)

and mount this filesystem on OpenBSD 7.7 in /etc/fstab:

192.168.130.2:/mnt/exportTest/ /mnt/exportTest nfs    rw,tcp,soft 0 0

the mount works well and I get:

root@bsdHost> ~# mount
...
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)

Within the filesystem there is a folder ssl-cert:

root@ubuntuHost:/mnt/exportTest# ls -aln
total 11
drwxr-xr-x  3 0   0  3 Jun 23 08:09 .
drwxr-xr-x 10 0   0 10 Jun 23 08:07 ..
drwxrwx---  2 0 114  2 Jun 23 08:09 ssl-cert

the folder looks like this on the OpenBSD host:

root@bsdHost> /mnt/exportTest# ls -aln
total 8
drwxr-xr-x  3 0  0      3 Jun 23 08:09 .
drwxr-xr-x  5 0  0    512 Jun 23 08:15 ..
drwxrwx---  2 0  114    2 Jun 23 08:09 ssl-cert

There is a user _openldap on the OpenBSD host who is a member of the group 114:

root@bsdHost> /mnt/exportTest# id -G _openldap
544 114

In my opinion, this user should be able to read the folder /mnt/exportTest/ssl-cert/, but:

root@bsdHost> ~# su - _openldap
No home directory /nonexistent!
Logging in with home = "/".
bsdHost$ ls /mnt/exportTest/ssl-cert/
ls: /mnt/exportTest/ssl-cert/: Permission denied

What also confuses me is, that the filesystem can be mounted multiple times:

root@bsdHost> ~# mount /mnt/exportTest/
nfs server 192.168.130.2:/mnt/exportTest/: not responding
nfs server 192.168.130.2:/mnt/exportTest/: is alive again
root@bsdHost> ~# mount /mnt/exportTest/
root@bsdHost> ~# mount /mnt/exportTest/
root@bsdHost> ~# mount /mnt/exportTest/
root@bsdHost> ~# mount /mnt/exportTest/
root@bsdHost> ~# mount /mnt/exportTest/
nfs server 192.168.130.2:/mnt/exportTest/: not responding
nfs server 192.168.130.2:/mnt/exportTest/: is alive again
root@bsdHost> ~# mount
...
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)
192.168.130.2:/mnt/exportTest/ on /mnt/exportTest type nfs (v3, tcp, soft, timeo=100)