You will definitely need an exit stamp from the EU when heading to the UK... Without it you are going to find it difficult to re-enter the EU next time as they will not be able to confirm the 90/180 rule. This still relies on old fashioned passport stamps to tot up the days...
​Although the French authorities may have an electronic record of your exit, this is not necessarily visible across the bloc, so should you try to re-enter anywhere other than France, you will definitely run into issues.
This should be resolved, and passport stamping will cease when the EU ETIAS system goes live (eventually).