Magento is not designed to operate against a cluster like PXC or even Group Replication. I would ensure that all Magento connections to your database are to a single instance.
You could switch out HAProxy for ProxySQL which would allow you to block specific queries and just always return true.
You could also try setting wsrep_osu_method=NBO to improve metadata locks.
I would also reach out to Magento support (since you pay for a license) and ask them what are their recommended settings for PXC.