Normal.
Seeing a food spike after eating is normal. Usually in the +2 to +3 time frame. ECID though.
Cat could have eaten a bit more, or a bit less. Digestion could have been slower or faster. You got a venous blood sample instead of a capillary blood sample. Cat got more exercise by running up and down the stairs 1 less time, or saw a squirrel at the window and ran from room to room like crazy cat to keep track of said squirrel so used less/more energy. Maybe Socks scarfed up some people food someone dropped on the floor or got into the dog's kibble (don't even know if you have a dog, but things happen)!
Don't get too hung up on the exact numbers.
First of all, remember that meters only have to read within 15% of a lab based reading to be considered accurate enough. So, that 270 BG reading +/-15% could have been anywhere in the range of 230 to 310 and would essentially be considered to be the same reading. That 340 BG reading +/-15% could have been anywhere in the range of 290 to 390 and be considered to be the same reading. So those readings you gave as an example are not that far apart.
Independent study in 2018 found that 2/3 of human glucometers approved by the FDA did not meet the FDA accuracy standards.
https://www.diabetesdaily.com/blog/not-all-fda-approved-glucose-meters-on-the-market-meet-accuracy-standards-581567/
Yes, I see that your spreadsheet shows you switched from the Alphatrak to one of the Relion meters but you use them randomly, still testing with both meters sometimes. That can get confusing. You might want to consider picking one meter and sticking to it.
Informative article from the Mayo Clinic on monitor accuracy here.
https://www.mayoclinic.org/diseases-conditions/diabetes/expert-answers/blood-glucose-monitors/faq-20057902 Yes, it talks about some of the inaccuracy factors for humans, but think if some of these could be happening with Socks.
Also, looks like the color coding on your spreadsheet is messed up. At least on the Relion 2019 version.
@Marje and Gracie used to fix those sorts of issues for people. Not sure if she still does that, but I've tagged her on this to see if she has time to help.
That PlaqueOff you are using is a seaweed, Ascophyllum Nodosum. According to
this article in Frontiers in Science, it's 44% carbs, give or take a couple of percentage points. That could be influencing the BG readings.
Bottom line, we really don't know why the readings are different from test to test. What we are looking for are patterns in BG readings but more importantly, is your cat Socks acting and feeling better?
Less pee in the litter box? Playing? Purring? Pooping ok? Good appetite? All good signs.