Routing

Hello, I have a most peculiar problem with my SRX 550 which I haven't been able to resolve after working on the problem for several weeks now.  
I've been trying to find an appropriate community for this, so apologies if I ended up in the wrong place. 

Problem: Specific VLAN(s) have intermittent packet loss during the day. We don't see it so clearly with ping, but are instead using VSee Network Test  to measure client issues with conference calls. 

This is a branch with around 500+ clients where the majority is on VLAN 8 connected with EX 2200 switches. Other clients are spread out on smaller VLANs that don't experience this problem. 

VLAN 8: 192.168.8.0/21 (became Client_wired)

Spliting the network
One of the steps i did was split off all wireless clients and wired clients into VLAN 8 and VLAN 16. But that didn't change things. Both VLANs kept experiencing intermittent packet loss. 

VLAN 16: 192.168.16.0/21 (became client_wireless)

Changing public IP on VLAN 8
The next thing i tried was when i changed public IP on VLAN 8 (NAT). Poof, all packet loss disappeared. Then i changed the public VLAN of VLAN 8 to the same public IP ... both networks experienced the packet loss issue again. 

Changing public IP on both VLAN 8 and 16

So I changed both networks to new fresh seperate public IPs...

VLAN 8 now experience no packet loss. This is the wired network where least clients reside. (around 50)
VLAN 16 still experience packet loss. This is the wireless network where most clients reside (around 500)

How can this be? How is NAT/public IP connected to this issue? Why does the issue follow whatever vlan/subnet that have the same nat as vlan 8? 
Does anyone have any insight what might be the root cause of this? Is it a L2 issue or a L3 issue? Is a client causing this? Is there some NAT issue or limit i'm unaware of?
One interesting thing on the VSEE test is that it indicates download packet loss, but not upload packet loss (although im not sure about the accuracy of this). 

Any tips are appreciated!