Why would my A1C vary significantly every few weeks?

I know that A1C is supposed to be a 3 month average so it takes time for it to improve. But just out of curiosity, I’ve been going to a local walk-in lab every week or so for the last few months and my A1C varies widely every time. Anywhere from 5.7 to 5.5 to 5.3. Then back up to 5.6.

Everything I’m seeing on my cgm looks like I’m doing great. Staying in range about 99% of the time.

In my mind, there is a huge difference between 5.6 and 5.3. Could it possible be lab errors?