These warning messages appear in _features_override_set_additions() and _features_override_set_deletions().
The foreach in both these functions is being passed (possibly due to improper creation of feature overrides?) single strings, single ints, classes (which is ok), arrays, and arrays that qualify as isset() but would fail on !empty().
The single strings (of value '0', string length 1), single ints, and arrays that are empty() are all throwing warnings when foreach tries to process them.
Are all data types acceptable parameters for argument 1 of _features_override_set_additions()? Knowing what the expected data types are for this parameter will help me save some time while troubleshooting this on my end.