What challenges do therapists see between sessions?

For occupational therapists and other rehabilitation professionals:
I’m interested in understanding what happens between therapy sessions.
From your experience:
• What are the biggest challenges clients face between sessions?
• Is it difficult for therapists to know whether clients are actually completing their activities at home?
• Would having a way to monitor progress between sessions be useful?
• What concerns would you have about using an app for this?
I’m exploring an early-stage idea and would really appreciate hearing different professional perspectives.