We would like to thank Lorenzo Foscolo, Mark Haskins, and Shouhei Honda for helpful discussions. We are also grateful to Hans-Joachim Hein and Jeff Viaclovsky for the stimulating discussions on the study of collapsing hyperkähler metrics on K3 surfaces which led to an earlier joint paper [HSVZ18]. We thank Yang Li for communications regarding the draft of his preprint [Li19] and the rough draft of the current paper in January 2019. Substantial parts of this paper were written when the second author was visiting Princeton University, Sinica Academia and ShanghaiTech University in the academic year 2018-2019. He would like to acknowledge the hospitality and support of those institutions.