Earlier quoted context omitted.
It's because the earliest RSUs they issued are expiring this year: https://www.theinformation.com/articles/stripes-early-stock-...
They’re options that are set to expire, not RSUs. Yes, the employees could exercise them to prevent them from expiring, but then Uncle Sam comes to collect his dues. And that’s where illiquidity burns you.
Both options and RSUs are required by law to have expiration dates. And it's plausible that either or both could have expiration dates within the next 12 months.