I did a little research and I found that it is used in the Netherlands and so it it either
Dutch or West Frisian. A somewhat known namesake is the late
Dutch economist Lense Koopmans.
My first guess was yet another short form of
Leonhard (Lennert,
Len, Lenzo, etc) and my second guess a short form of names containing LAND, but the
Dutch Given Name Database (NVB) disagrees: They analyse it as a Frisian short form of names containing the name element LIND [1]. I consider the NVB a reliable source and discard my guesses for that reason.
--elbowin
[1]
https://www.meertens.knaw.nl/nvb/verklaring/naam/Lense