[exim] exim 4.89 + "no host found for existing SMTP connecti…

Hello list,

after switching to a new upstream mailprovider we see tons of
"T=remote_smtp defer (-53): no host found for existing SMTP connection"
in our log, comming from a manual router which passes all remaining
mails to the provider:

send_to_gateway:
driver = manualroute
transport = remote_smtp
route_list = * smtp.provider.example

smtp.provider.example usualy resolves to a _different_ A record on each dns
query (4-5 in total) but does NOT do dns round robin (does not return a list
of records but a single entry each time).

Any ideas how to fix this issue on our side?