Conversion between pounds and euros when a MCIF is finishing

Dear members of the MCAA UK chapter,

I will finish a MC individual fellowship in few months. In my fellowship there was something unfortunate: the fellowship was signed before Brexit (March 2016) but took place after it (April 2017-April 2019). For that reason, the pound-to-euro conversion used during the whole contract (1.45, before Brexit) was much higher than the actual conversion rate (around 1.15, after Brexit). As you can gues, this makes a quite a difference. Related to this situation, I have some few questions:

1. With respect to the administration of the funding, how is the conversion to other currencies work? Is the whole money converted at the date of signature, or at the starting date, or is this done on a monthly basis (or other time interval) during the contract?

2. What should happen if, due to conversion issues, there is remaining money at the end of the contract? Is this regulated by the EU, or is this addressed idiosincratically by each institution?

Many thanks!

Fernando