I would go with singular, but the verbal reference is to "loss", not "conversion". If the sentence is in context of referring to multiple losses from a single conversion, then it would be plural. If during the conversion 12 widgets were lost, then I would use singular. If 12 widgets were lost, plus a loss of time, plus a loss of money, it could be correct to use plural.
I agree that the reference is to "net loss", not conversion. I think singular because "net" refers to a single loss measurement -- the difference from starting condition to ending condition -- even if that entails multiple step losses in between.
It would still be singular even if you referred to multiple conversions: "the net loss after 15 conversions was 7%"
(But I'm a software guy, not a grammar dude... And I panic a little bit even posting this, fearful of the grammar offences this post itself might contain. Like starting a sentence with "And". And apparently it can be spelled "offences" or "offenses", and I'm not sure which of the two is proper for American English...)
Yes, we are agreed that the subject "loss(es)" sets the plurality for the rest of the simple sentence.
The question is whether the adjective "net" determines whether the subject noun "loss(es)" is singular or plural. The adjective " net" conveys the idea of one descriptor for a number of things ("steps").
What about "The net losses from the rwo-step conversion were 4%."
"net" is "remaining after the deduction of all charges, outlay, or loss" so I still think it depends how the sentence fits in context with surrounding sentences. If different types or quantities of losses occur, it would make sense to have it plural. If the losses fall under one description, make it singular.
This takes me back to 7th grade (early 1960s) and diagramming sentences.
Both sentences are grammatically correct, at least as far as subject/predicate noun/verb agreement: "loss" is singular and requires the verb "were," and "losses" is plural and requires the verb All other parts of the sentence are qualifiers and can be ignored.
"Net" has nothing to do with anything because adjectives don't affect (not "effect") the noun/verb agreement.
Finally, if you are concerned about whether "net loss" or "net losses" is correct, that is not a grammar question but instead depends on what you are trying to say. If you are describing the sum of all losses of a single type (like a profit/loss statement), then it would be "net loss." If you are describing multiple independent losses, then "net losses" might be more appropriate.
Most situations would probably be better covered by using "net loss."
Atom12 posted while I was writing, and I agree with his "loss" vs. "losses" statement.
Either one is correct, in it's appropriate context. If there was one loss then the first one is correct. If there were more than one loss then the second one is correct. The verb has to match the subject, but the subject is defined by the situation, not by the sentence that contains it.
Re: 'Sony are' and 'Sony is', I believe that either is correct depending on the intent of the writer.
I recall from an advanced English language course I did some 30 years ago (not at a Uni but at a similar to Uni level) where there was an exploration about the times when a singular or plural verb could be used after a collective subject. For example, 'The audience is clapping ...' or 'The audience are clapping ...'. It depends on whether the writer's intent relates to the subject being a collective as a whole (i.e. Sony as an organisation; or the audience as a collective of the group of people) - then the singular verb can be used.
But if the subject represents the units of the collective (i.e. all the individuals that make up the management and/or staff of Sony; or all the individual persons that make up the audience), then the plural verb can be used.
My pet hate: the use of 'less' when 'fewer' should used. Less relates to quantity, but fewer relates to numbers. While we may hear "There were less emails today than yesterday", at least we don't hear "There is fewer flour in this pack than the other pack".