Hello,
Thank you for your question.
Reason why you can’t isolate VLANS is that by default VLANS are created in the same zone as LAN network, that’s why you can reach them.
To solve it you will need to remove your VLANS from LAN zone, create your firewall zone for new VLANS on your device and reject forwarding, then you will not be able to ping different VLANS. Follow the article below to separate VLAN zones. After completing configuration restart firewall or devices, because new rules will not apply after changes.
In previous ticked I gave you configuration example for VLANS, follow steps from there.
Previous response: RUTX50 VLAN config - Teltonika Networks - Teltonika Community
Best regards,
Eimantas