It's hard for me to answer. All I can tell you is that for whichever backup profile this screenshot refers to, the part size is 2047MiB. Any backup smaller than this will be a single file.
The only other ticket you have filed under your user account does not talk about split archives at all. Since we had not discussed this setting previously, I don't know what it was set to in the past. I can infer that it probably wasn't 2047 MiB because a 40+ part archive with this part size would be 80+ GiB — I think you'd have told me upfront if you had such a gigantic backup archive, right?
Conversely, since you have a split backup archive check what is the size of the .j01 file. That's the first part file of the backup set (.jpa is the last). The size of the .j01 file is the part size you had set up. Make sure to divide the size in bytes with 1,048,576 to come up with the value in MiB. Note that Windows and macOS (and some Linux desktop environments) use base-10 megabytes (1,000,000 bytes in 1 MB) instead of base-2 megabytes (1,048,576 bytes in 1 MiB). Akeeba Backup uses base-2 megabytes.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!