Since the upgrade to Koha 3.18 our librarians can't use Batch item modification tool as always. They can change values from something different to "0" to something different to "0", but no change the value to zero or remove the subfield.
How to test:
1) Go to Batch item modification tool (for eg http://demo-intra.mykoha.co.nz/cgi-bin/koha/tools/batchMod.pl )
2) Paste a barcode (eg 528, «The ringmaster's secret», without hold/loan).
3) Change for example $7 (Not for loan) and/or $8 (Collection code) to a !=0 value, lets say Ordered and Non fiction.
4) Repeat same procedure but now delete subfields.
5) Subfield is not removed.

Same thing if you have an authorized value "0" and try to change to that value. Changing from !=0 to !=0 works fine.