`TypeError: Cannot read properties of undefined (reading '_s')`

[bilogic]

Refer this example: https://stackblitz.com/edit/vite-a3mv97?file=docs/.vitepress/theme/index.ts,docs/counterStore.ts,docs/index.md,docs/ssrStorage.ts

Originally posted by @brc-dd in #2672

I'm having the same TypeError: Cannot read properties of undefined (reading '_s')
Can the solution be explained please?