Issues

Config generated by Proxmox 6 Web UI.

Main network 192.168.64.0 and VLAN 28 network works OK. No connectivity from VMs/CT connected to vmbr0

/etc/network/interfaces

auto lo
iface lo inet loopback

iface enp34s0 inet manual

auto vmbr0
iface vmbr0 inet static
	address 192.168.65.123/21
	gateway 192.168.64.1
	bridge-ports enp34s0
	bridge-stp off
	bridge-fd 0
	bridge-vlan-aware yes
	bridge-vids 2-4094
	network 192.168.64.0

auto admin
iface admin inet static
	address 192.168.28.232/22
	vlan-id 28
	vlan-raw-device enp34s0
#ADMIN vlan

Config copied from another proxmox machine where everything works ok. On this machine works only connectivity with 192.168.64.0. Packets from VLAN28 are dropped on vmbr0

# the PVE managed interfaces into external files!

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

iface enp34s0 inet manual

auto vmbr0.28
iface vmbr0.28 inet static
        address 192.168.28.232
        netmask 255.255.252.0
#        gateway 192.168.28.1

auto vmbr0
iface vmbr0 inet static
	address 192.168.65.123/21
	network 192.168.64.0
	gateway 192.168.64.1
	bridge-ports enp34s0
	bridge-stp off
	bridge-fd 0
	bridge-vlan-aware yes

On first system where everything works well:

02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)
	Subsystem: Micro-Star International Co., Ltd. [MSI] RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
	Flags: bus master, fast devsel, latency 0, IRQ 17
	I/O ports at e000 [size=256]
	Memory at f7c04000 (64-bit, prefetchable) [size=4K]
	Memory at f7c00000 (64-bit, prefetchable) [size=16K]
	Capabilities: [40] Power Management version 3
	Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit+
	Capabilities: [70] Express Endpoint, MSI 01
	Capabilities: [b0] MSI-X: Enable+ Count=4 Masked-
	Capabilities: [d0] Vital Product Data
	Capabilities: [100] Advanced Error Reporting
	Capabilities: [140] Virtual Channel
	Capabilities: [160] Device Serial Number 01-00-00-00-68-4c-e0-00
	Kernel driver in use: r8169
	Kernel modules: r8169

2nd system where there is problem with bridge and vlans:

22:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15)
	Subsystem: Micro-Star International Co., Ltd. [MSI] RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
	Flags: bus master, fast devsel, latency 0, IRQ 35
	I/O ports at f000 [size=256]
	Memory at f7504000 (64-bit, non-prefetchable) [size=4K]
	Memory at f7500000 (64-bit, non-prefetchable) [size=16K]
	Capabilities: [40] Power Management version 3
	Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit+
	Capabilities: [70] Express Endpoint, MSI 01
	Capabilities: [b0] MSI-X: Enable+ Count=4 Masked-
	Capabilities: [100] Advanced Error Reporting
	Capabilities: [140] Virtual Channel
	Capabilities: [160] Device Serial Number 01-00-00-00-68-4c-e0-00
	Capabilities: [170] Latency Tolerance Reporting
	Capabilities: [178] L1 PM Substates
	Kernel driver in use: r8169
	Kernel modules: r8169