I have a VLAN configuration problem and would like some advice.

Background:

My router (not a TP-Link model) is configured with four subnets (primary network, IoT network, camera network, and media network).  All the LAN ports on the router are configured as trunk ports with the primary network untagged and the other networks having VLAN IDs of 30, 40, and 50 respectively.  One of the LAN ports is wired to a TL-SG116E Easy Smart switch which feeds all the devices in my home office area.

The TL-SG116E is configured for 802.1Q VLAN tagging and the trunk port from the router is connected to Port 1.  Port 1 is untagged for the default VLAN and tagged for the remaining VLANs.

The remaining ports are configured as follows:

Ports 2 through 6 are untagged members of the default VLAN (PVID=1).

Ports 7 and 8 are untagged members of the IoT VLAN (PVID=30).

Ports 9 through 12 are untagged members of the camera VLAN (PVID=40).

Ports 13 through 16 are untagged members of the media VLAN (PVID=50).

With the above configuration in mind, I have a Synology NAS that features two LAN ports.  The primary port is connected to the primary network (Port 3 on the switch).  The idea here is to configure the second LAN port of the NAS with an IP address on the camera network so that my NVR (which also resides on the camera network) can back up files to the NAS without having to route everything back through the router.  It should then be a simple matter of connecting the second LAN port to Port 10 of the switch.

Problem:

The problem I ran into in the past with the above configuration was that network loops were randomly occurring, causing everything to freeze.  For a lack of time, I never determined whether it was the switch or the NAS that was causing the loops.  Yesterday, I tested the configuration and over a period of several hours, everything was working fine and there were no issues.

I have found information on the internet which says two devices should not have two Layer 2 paths between them.  I don’t know if this applies in this case where VLANs are used.  I also don’t exactly know how the TP-Link Easy Smart switches handle Layer 2 VLAN traffic (i.e. separate MAC tables for each VLAN, etc.).  Can someone shed some light on this and perhaps give me some advice on the proposed configuration?