It probably won’t be fixed for the next version (if it even gets released at all). This issue appeared after updating the underlying Smack library and it seems to be fairly complex to fix. In nightly builds of 2.9.0 there is a setting to force IBB transfer. Which is slower, but might work in this scenario. It is in Preferences > File transfer. Nightlies are here https://www.igniterealtime.org/downloads/nightly_spark.jsp
And here is a ticket associated with the degraded file transfer issue https://issues.igniterealtime.org/browse/SPARK-1869