I used a protocol to extract proteins from a soluble and insoluble fractions obtained from mice livers, based on this publication

Schmidt BZ, Perlmutter DH. Grp78, Grp94, and Grp170 interact with alpha1-antitrypsin mutants that are retained in the endoplasmic reticulum. Am J Physiol Gastrointest Liver Physiol. 2005 Sep;289(3):G444-55. doi: 10.1152/ajpgi.00237.2004. Epub 2005 Apr 21. PMID: 15845869.

After centrifugation, you take the surnatant, that contains the soluble fraction, and the remained pellet, cointaining the insoluble fraction, is resuspended in a buffer composed of 50mM Tris-HCl pH6.8, 5% SDS and 10% glycerol, followed by sonication for 1 min and boiling at 95°C for 10 min. Problem is, at the end I still find the pellet not well resuspended, moreover if I put the samples in the ice, the solution solifies as oil when refrigereted at 4°C or lower, and I need to warm up the sample and vortex it to make it liquid-ish again. How can I improve the protocol to better resuspend the insoluble fraction?