Having recently reread both series I can’t tell how they’re related. Is it perhaps from unfinished chapters of Kibishii no de Aru? I didn’t see any of the same characters in these stories.

Some characters appear in both works: Chikara Ogawa appears as a main character in Kibishii no de Aru and briefly in Yume ga Kanau Juunigatsu. For Kubo, it's the other way around.

So, in a way, the manga are connected because most of the stories revolve around people from the same workplace i.e. Chikara works as a designer for Kubo's company, is under Kubo's supervision, and has a brief fling with Kubo.