Avoid logging for missing backends

[alecandido]

As they may also be part of a backend search loop.

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.93%. Comparing base (9863ca1) to head (95c71fa).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1486   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files          81       81           
  Lines       11792    11792           
=======================================
  Hits        11784    11784           
  Misses          8        8           

Flag	Coverage Δ
unittests	99.93% <100.00%> (ø)

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[scarrazza]

Thanks, works perfectly.