Good suggestions, especially about more testing with a regular BG meter to watch post-prandial reactions to certain foods. It looks like you already have a restricted eating window too, using BPC, a good plan. Agree that 5.7 is nothing to worry about, labs do use different ranges but often "pre-diabetes" is 5.7 to 6.4 , so some minor variation from the sample or lab tech reading the results could move you from very lowest of the "pre" to perfectly normal.

And Chris Kresser has reasons that HbA1c might not be all that its cracked up to be, especially for LCers. Having a computer count amount of sugar stuck to RB cells seems to me a test open to variation. https://chriskresser.com/why-hemogl...eliable-marker/

You have done very well losing 28 pounds in 9 months, but it is also possible that you have not resolved your insulin resistance yet. A waist to height ratio less than half is one simple indication of IR, and at the same height, gender and near in age, it takes a while to get metabolically healthy.

Hang in there, you are doing well, don't let one tiny point on a large number range define you. Were other numbers OK? Was there a Fasting BG also lab tested? What about fasting insulin? (Not common, but some LC doctors add it to the usual lab tests). Lipids? Liver?
How to do feel, happy on your LC plan? Other health improvements? Check your health holistically and you likely are much better than 9 months ago!