On slow network connections, users authenticated by LDAP are not assigned to groups

We have be struggling with intermittent problems with LDAP on users' desktop Ubuntu PCs. When they log in, they are often not added to any groups apart from their matching user group, e.g. "john" would only be assigned to the "john" group but should also be in "adm". We enabled logging in nslcd.conf and observed that user group data was being received, it just wasn't being used.

We have separately discovered that those PCs were only connecting to the local network at 100MBits due to a cable problem. This issue has been resolved and now that the PCs connect at 1000MBits, the LDAP groups problem has gone away.

I believe there is a race condition bug when user sessions are created.

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: libnss-ldapd 0.9.10-2
ProcVersionSignature: Ubuntu 5.0.0-15.16-generic 5.0.6
Uname: Linux 5.0.0-15-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.20.10-0ubuntu27
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu May 16 12:19:08 2019
InstallationDate: Installed on 2019-02-25 (79 days ago)
InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3)
SourcePackage: nss-pam-ldapd
UpgradeStatus: Upgraded to disco on 2019-04-23 (22 days ago)