One day for a work event (I masked all day) and I'm on day four. Hopefully just a bad cold and not COVID. Hope you're doing better soon!

Not mandating masks in healthcare settings seems completely insane.

Fun fact for tiny build fans, Ethernet cables have a minimum length to achieve their stated performance.

Yeah. They won't support it if you have a fault so keep the default in a box somewhere, but it's officially kosher to provide your own. You'll get a box on the wall (ONT) that turns PON fibre into gigabit ethernet, and that you have to use. But it's essentially a media converter. DHCP is all you need, no authentication/login - your ONT authenticates you.

Used to work there. It's fine, esp on the newer builds which you'll be in. XGS-PON and usually plenty of backhaul capacity. Router's crap, chuck it and buy something decent, same as any other ISP.

Blocking ICMP entirely is a recipe for weird stuff happening. There's some ICMP worth blocking - redirects, etc - but turning it off entirely A) makes debugging stuff a nightmare and B) can break some things entirely e.g. MTU probing.

Sounds like firewall fuckery. Something doing too much DPI on some interesting looking packets that can't cope with the volume, choking and dropping what it can't handle. Check packet loss while this is happening and look real close at the Fortigates. Could also be MTU fun with IPsec in the mix.