Lantus: ? Batch fault

I have read an earlier post(2000) about Lantus causing a sudden drop in blood sugars because of injecting in a fatty site.
My problem was a blood sugar running at 3.5-4 over 3 days, feeling off but not ill as such. It was a new box of pens that were manufactured for Europe and not UK. They had stickers on the pen with batch no’s, date and dose. Could it be the batch? Unfortunately I have 10 pens (2boxes) of the same batch nos. Could it cause this drop, I normally run 6.5 - 8?
Will the chemist swap it or not.?

Antje77 said:

This is definitely not the dreaded drop you've read about, but mistakes are made everywhere, even in insulin production. Do you have pens from another batch to try?
Of course it could also be the weather, your period coming up, a miscalculation in the carbs you ate or the color of your socks.

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I have tried another pen from a different box/ batch no’s and sugars seem to be under control today. Cannot relate it to anything else. Just Cross I have 2 boxes of the same batch nos. Gp’s will say I have had a prescription and may not give me another one.