Cutepally:

Supply the following if possible:

• Device problem occurs on: NETGEAR WNDR3700v4, most likely others which also use mac80211.
• Software versions of OpenWrt/LEDE release, packages, etc: Builds since r9645 till today at r9900.
• Steps to reproduce: use some monitor tool in openwrt. bully, reaver, hcxdumptool, etc. they all cause the problem.

ok, so. it's been about a month or so, this problem has been happening but i finally gathered the time to narrow it down.

message: mac80211: optimize skb resizing to avoid reallocation when using 802.11s + batman-adv
commit: 60659b2
author: Felix Fietkau

this patch (openwrt/package/kernel/mac80211/patches/subsys/357-mac80211-optimize-skb-resizing.patch) will cause the router to reboot anytime you use some monitoring tool like hcxdumptool.
the issue started at 60659b2 and continues to be a problem. it was modified in:

message: mac80211: update to version 4.19.32-1
commit: 3183430
author: Hauke Mehrtens

but the issue is only with this file (openwrt/package/kernel/mac80211/patches/subsys/357-mac80211-optimize-skb-resizing.patch)
on r9900 if i remove this file and build an image all these tools are working again without a reboot.
something to do with this file needs to be reworked but sadly, i don't know enough to help with that but i narrowed it down to this file.
i hope this is enough :) thank you everyone <3