Unable to successfully call PETSc function 'VecCreate'

Hey guys, I am running a code to compute time dependent functions using implicit Euler scheme and I need to convert the function solution into a vector using the Function.vector() attribute as you can see an example below:

self._etaf = etaf0.copy()

#Building local base functions etaf
A = assemble(self._aa)
  
Af = A.copy()
self._fv = assemble(self._LL)
  
[bc.apply(Af, self._fv) for bc in self._bcs]
              
U = self._etaf.vector()
  
  
solve(Af, U, self._fv)

In my case etaf0 is a copy of Function(V) where V is the mesh. The forms self._aa and self._LL are defined and U is the vector. When I run lots of iterations, I have to write U everytime to solve the linear system Af*U = fv. However, I am getting the following message at some point of the iterations

Unable to successfully call PETSc function ‘VecCreate’

Does anyone know why this is happening? If this was answered somewhere else I would be thankful to get the link to it.

Thank ypu very much in advance!

See for instance: MPI communicators remain blocked - #8 by beschlcc