Sudden drop in review number

I seem to have had a sudden drop in review number and was wondering if this was a glitch? I used to average 200-300 reviews a day but at the moment I seem to only be offered under 100. Has anyone else experienced this? I have adjusted my settings so that I can do maximum number of reviews. I have over 4000 cards so I’m certain I should not receive such a low number of reviews a day.
Any help would be appreciated