Something changed about XP Boosts. Now, how can you tell which lesson activates a boost?

Before, completing the last lesson of a group (e.g. completing 5 of 5) activated a 15 minute boost. Which allowed me stop doing lessons at 4/5 and do practice instead. Later that day, I could complete lesson 5 to get a boost for a new session.

Now, these activation steps seem to be randomly scattered across lessons. Sometimes it's lesson 2, sometimes 5. Never the last one.

Did anyone else notice this? Any idea why? How do you deal with it?

It leads me to learn longer than I actually wanted (because I accidentally trigger boosts), or leads to me 'wasting' boosts, both of which feels bad.