Hi Dale,
I took a quick look at the manual, but also didn't see SIP ALG. Note however that it needs to be off on both ends to work, so
only looking at one side's router isn't enough.
Try it remotely from a different location and see if the problem persists. If it does, then I suggest that you replace your router.
This is actually quite common, since a lot of routers out there are garbage.
I can also take a Teamviewer look if needed, but am in the process of moving from Germany to Florida and still working at the
same time, so time is tight right now.
73,
Mitch DJ0QN / K7DX