There are at least two things wrong here:
Your router (192.168.55.1) does not have a route to 192.168.75.0. You need to configure this route on your gateway router.
You've created a DHCP server for the local subnet, but you also have ip helper configured on the router interface. Pick one or the other.
I routed traffic from 192.168.75.0 to 192.168.55.38
ip route 192.168.75.0 255.255.255.0 192.168.55.38
What you're doing here might break connectivity for the local subnet. Note that the first parameter is the destination network prefix, not the source. To set up the default route, use 0.0.0.0/0 as destination (likely you've done that already long since), e....
You would only use a loopback for layer-3 switches that have routing enabled because you must route to and from the loopback interface.
Layer-2 switches use an SVI and default gateway for management because there is no routing on a layer-2 switch to be able to reach a loopback interface.
Assuming you refer to NAT/NAPT.
Possible? Definitely. You can use a boundary NAT router and then route between VLANs plainly.
Acceptable? That depends on your requirements and policies. NAT is normally only deemed acceptable when there's a real need to translate addresses, e.g. between public and private address space. Since NAT breaks the original end-to-...
should I configure vlans in my netgate at layer 3, or implement it on my switches at layer 2?
Configuring VLANs on the switches separates those subnets from each other, so they can't communicate with each other without a router/gateway.
From the center switch, configure the link to the pfSense as a VLAN trunk, with all VLANs tagged. On the pfSense, ...
Unless you have access interfaces on VLAN 1 (not good to use VLAN 1 or a native VLAN) connected to the layer-2 access switch, you do not need to trunk VLAN 1 to the access switch. The gateway on VLAN 20 will route traffic between VLAN 20 and VLAN 1.
To let the hosts on VLAN 20 get DHCP from a server on VLAN 1, you use the ip helper-address interface command ...
I'm adding an answer to the question as the supplier found the solution to the issue we were experiencing. I'm merely adding here his explanation, it could be useful to anyone else incurring in this event. Thank you again!
[13 April 2021 12:31]
I found the solution that you need to add the Virtual MAC address on one of the interfaces of both EDR.