BibTeX does not have the right entry for preprints. This is a hack for producing the correct reference:
@Booklet{EasyChair:931,
author = {Dmitry Luchinsky and Halyna Hafiychuk and Miroslav Barabash and Vasyl Hafiychuk and Taku Ozawa and Kevin Wheeler and Peter McClintock},
title = {Atomistic model of reptation at polymer interfaces},
howpublished = {EasyChair Preprint no. 931},
doi = {10.29007/m5hf},
year = {EasyChair, 2019}}