Hello,
I see that Vendors come to SRX300 on irb.453 and Guests come on irb.454. On same interfaces, address assignment also happens as per configuration.
Are irb.451 and irb.452 part of another VR or inet.0?
Do you have route leaking properly configured between routing-instances for reverse direction flow?
You can take 'security flow traceoptions' with proper packet-filter (to match the traffic) to see where the packet is getting dropped.
Regards,
Rushi