Spike S2 domain can not be visible in the density map

hello,everyone,I am resolving a SARS-CoV-2 spike structure in CryoSparc ,I use blob pick(160-220 diameter),then 2D ,however,interestingly, 2D classfication can not see the S2 domain density,and the density of S1 domain(including NTD,RBD,SD1,SD2)is very clear . Is there a possibile solution? Is there any parameter adjustment available for particle selection and 2D classification? The parameters I have used so far are all default now. Thanks for helping me!