Was going to post the same thing. I had a new construction townhouse in the Bay Area that had Ethernet. The max speed was either 10 or 100 Mbps depending on which jack was used. Opened up the jacks to discover that the cables were stripped of the jacket for at least 6 inches, the twisted pairs were untwisted and this mess was jammed into the wall behind the jack. At every single location. The worst offender wouldn't connect at all. That had a foot of jacket stripped off. Re-crimping all the jacks made everything work at 1 gigabit.

In summary, general tradespeople don't know how to install Ethernet.

It probably only has 4 wires hooked up. That's all you need for 100 meg.

Despite claims to the contrary, gigabit will work over cat 5 (just not 5e!) in the majority of cases.

My best anecdote on that is when an Ethernet wallplug was punched down with a flat screwdriver... which worked as hardware firewall for the SMB traffic. Everything else worked fine: ICMP, HTTP/S... but not SMB. After I re-punched it with a proner Krone it started work fine for the SMB traffic just fine.

Yep, I had a cable that was working at gigabit, until it was pinched by a door and bent really hard. Then it started working at 100 MBPS.

Regular cat5 is only rated at 100mbit.

5e will handle gigabit, and I've seen 5 work for short runs too.