I think you're right, also I just saw this

https://participant-help.prolific.co/hc/en-gb/articles/360021785574-I-m-not-receiving-any-studies

"There's no need to worry though! It is unlikely there is anything wrong with your account unless you have:

Participated in a study and received an error code
Attempted to login and notified that your account is on hold
Not received studies in over two months

We also try to make study distribution fair so that participants get an equal chance to take part. If you've completed a lot of studies recently, you may find you'll be invited to fewer studies for a short period of time."