[FS#4003] VLAN interface drops default gateway, prompting interface restart (Attachment added)

[OpenWrt Bugs]

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A new Flyspray task has been opened.  Details are below. 

User who did this - Bitshiftnetau (bitshiftnetau) 

Attached to Project - OpenWrt/LEDE Project
Summary - VLAN interface drops default gateway, prompting interface restart
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - Device: raspberry pi 4b+
OpenWRT: SNAPSHOT r17101-f4e3ff5b07
Steps: 

1. setup rpi in AP mode
2. setup VLAN interface on br-lan and set the protocol to "DHCP client"
3. use the firewall rules to route from wlan to br-lan
4. wait an unspecified amount of time

Eventually the interface will drop the default gateway for some reason, reflected in the internet access on devices connected to the wlan. Restarting this VLAN interface will instantly fix the problem and connected devices can access the internet again. 
 
See attached config

One or more files have been attached.

More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=4003

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