A few things:
#1 don't call your bridge "LAN", before or later it will bite you, call it (say) "bridge_lan" or "bridge" or "bridge1"
#2 DO NOT use "detect internet" (set it to "none"), this is Rule #5
The twelve Rules of Mikrotik Club
#3 your interfaces are currently not categorized, they should normally be:
/interface list
add name=WAN
add name=MGMT
add name=LAN <- you see ... 
/interface list member
add interface=bridge_lan list=LAN
add interface=ether13_mgmt list=MGMT
add interface=sfp-sfpplus1_wan list=WAN
#4
/ip firewall nat
add action=masquerade chain=srcnat out-interface-list=WAN