It's better if you have a separate port in the OPNsense. Assign it, enable it, name it TRUNK and DO NOT assign an IP address to it. After this assign your VLANs to the TRUNK port as parent and connect it to the switch. The try to untag your VLANs to specific ports. Avoid to mix tagged and untagged traffic on the same port in BSD, especially if you use netmap(Sensei/Zenarmor)...