Probably unanswerable without knowing the details, i.e. which specific companies/bonds, details which haven't even been shared in that article. I'm sure Goldman and JP have good lawyers that have perused the sanctions, which (insofar) don't include all Russian assets. If you had more details, you could ask on law SE.
Relevant quote from the article though
At one major U.S. hedge fund, a decision was made to avoid Russian bonds entirely for now. The specter of holding debt that could become untradeable in another round of sanctions is too risky, and the war is just a week in.
Obviously some at Goldman and JP are betting not all Russian assets will be added, perhaps before some rebounce or they can find buyers, e.g. Chinese etc.
Generally speaking, larger companies like Goldman or JP have better compliance departments, which enables them to better weight risks like these.