The below blog post and thread have the relevant policies related to adding and removing members of ZCAP. Regarding the “use it or lose it” policy, the blog post states:
We are also adjusting the “use it or lose it” policy, as we feel that the previous policy of dropping members if they miss a single vote has resulted in some perverse effects. Going forward, ZCAP members who fail to vote in three consecutive ZCAP polls will be removed from ZCAP unless they have reasonable grounds for failing to vote. However, this policy will not apply to ZCAP members who would automatically be immediately eligible to rejoin ZCAP (e.g. contributors who have made a meaningful contribution to zcashd or Zebra).