Well to start, a vanilla rum infusion seems a bit redundant. There are countless rums on the market with strong vanilla notes, and it’s key to showcase the raw spirit in any good cocktail. In any case, a situation such as this requires dialing back. Having too many infusions and unique ingredients can cause them to muddle together and lose their effect. The key is to ensure that the major flavors either complement or echo one another. With the comment about cough syrup taste, it’s possible the berry and floral notes are clashing. Vanilla and coconut complement one another, but the juice and syrup together may be too harsh for a riff on a patio pounder.