[ODK Community] Default not working if question is skipped

The value of a field is empty / undefined if it is not relevant. It DOES
NOT assume the default value.

Typically, what you would do is repeat the relevant condition appropriately
in the logic for your new.mems calculation:

if (${totmem_check}=2, return-value appropriate-for-no-total_mem-value, if
(${total_mem}>...) )