I'm CP 210, ESO-Plus and tried a crownstore scroll of 150%-XP gain and finished some open missions.
In the beginning everthing went as expected: instead of 166k XP i got 250k and so on. But later, xp-gain diminished. In the end, every quest only awarded 19,5k xp (instead of f.e. 49k+ without the scroll).
Even after the scroll was used up, the effect was still present for the whole day: for daily crafting quest, I only got 866 instead of 3,3k.
Support says, it can't answer questions about game mechanics.
This looks like, there is a daily cap for experience gain, which shouldn't be there? Does anybody know, what went wrong?