VLAN troubleshooting is somewhat different than troubleshooting other network problems in that if you have an enterprise-level switch, the manufacturer will have troubleshooting guidelines tailored to the switch. You still need to verify that the pfSense component of your configuration is correct, however, and there are some troubleshooting elements that are common to all brands of switches. We will begin by considering general configuration issues.
General troubleshooting tips
It is good practice to work our way down on the OSI network model, which means starting at the Physical Layer. You should check your cabling, and if necessary, you should replace suspect cabling with known good cabling. Having a working time-domain reflectometer, ...