There is an article in the Edutopia website that addresses this question. The article isn’t peer-reviewed, but it is thoughtful. The source link is www.edutopia.org/blog/pbl-vs-pbl-vs-xbl-john-larmer.
This is a useful starting point for differentiating problem- from project-based learning. The original article published in 2014 and was later updated in 2015. The table in the article has colored my perception of the differences between the two pedagogies. Having said that, I doubt there is a universally agreed definition for each, and I am not sure that there needs to be one. For me, what will be important will be to cite (peer-reviewed) sources for my definitions and to settle on how I want to differentiate them, if I need to do that. I use mostly project-based learning activities in my courses when the subject matter fits this teaching method. These activities usually run through the full semester.
The following tabled is from the article by John Larmer mentioned above.