That seems to be an issue with Portainer then.
As said before, I'm not familiar with Portainer, but I recall some reports of others using it that Portainer would sometimes hold on to its configured parameters, despite restarting the container.
In those cases, throwing away the container and configuring a new one presumably has worked (see e.g. Pihole Portainer/Docker 5.8.1 startup error? - #16 by hNt).