UsingSynonyms doesn't work

UsingSynonyms doesnt work. Returns 0 results. Anything wrong with my syntax? I have tried appplying UsingSynonyms at the end of my query as well, same result.

We are not using Unifiedsearch by the way. We are searching for a specified <MyType>.

The query also adds in Boostmatching and Facets.

Version: 12.2.0

query = query.For(searchTerm, q =>
                {
                    q.Query = searchTerm;
                }).UsingSynonyms()
                    .InField(x => x.ItemName)
                    .AndInField(x => x.Code)
                    .AndInField(x => x.ParentCategoryNames)
                    .AndInField(x => x.ItemTradeMarkName)
                    .AndInField(x => x.ItemPrimaryVendorId)
                    .AndInField(x => x.ItemPc1VendorsitemId)
                    .AndInField(x => x.ItemEOProducer)
                    //.AndInField(x => x.ItemIngredience) //kommentert ut; SG-3276
                    .AndInField(x => x.ItemPc2AdvertisingText);
                if (trackSearchTerm)
                {
                    query = query.Track();
                }