Bugfix: accumulated grad batches [wip]

[Borda]

What does this PR do?

TODO: change the destination branch to master

Fixes # (issue)

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[codecov]

Codecov Report

Merging #5182 (8bb74cd) into bugfix/5165_enable_pl_optimizer (85e4e96) will decrease coverage by 61%.
The diff coverage is n/a.

@@                        Coverage Diff                        @@
##           bugfix/5165_enable_pl_optimizer   #5182     +/-   ##
=================================================================
- Coverage                               93%     32%    -61%     
=================================================================
  Files                                  134     134             
  Lines                                 9931    9793    -138     
=================================================================
- Hits                                  9245    3149   -6096     
- Misses                                 686    6644   +5958     

[Borda]

closing in favor of #5191