Hello, welcome!
I was told many years ago to take levemir once a day and for the last couple of years, levemir is better when taken with split doses. I agree it works for like 18 hrs or so and slowly tapers off. With split levemir, you can adjust either morning or evening dose and to make sure it is working is to do the basal testing. Where you fast, let's say after dinner, so no fast acting insulin on board, do 1 test at midnight and another test at 3am to make sure it is doing it's job.
I had difficulties with levemir because I was hypoing no matter how I adjusted it so I was prescribed Tresiba to combat nocturnal hypos. which apparently is similar to lantus
have you spoken to your DSN or consultant about it?