The zero maximum, also showing as the "Attainable" in the graphic, is a reporting bug introduced a few weeks ago. Nothing to worry about.
The important things you are looking for are the IP Profile, which shouldn't vary much, and the download speed which the better the ISP the closer it stays to the IP Profile. If the difference between them is big, or varies a lot, then that's not good.
Figures are only really trustworthy using a wired connection if you want to see how your ISP is performing. Wireless connection is often subject to wild swings due to other connections in your neighbourhood, microwave ovens, and a host of other things.
My broadband basic info/help site - www.robertos.me.uk
| Domains,website and mail hosting - Tsohost
Connection - Plusnet
Extra Fibre (FTTC). Sync ~ 54.0/14.9Mbps @ 600m. - BQM
"Where talent is a dwarf, self-esteem is a giant."
- Jean-Antoine Petit-Senn.
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.