I had a couple strange issue's with 1903 in the beginning like, clicking Apps in the settings menu would just disappear.  After the first round of updates 2 weeks back, I haven't had any further problems.

On my i7 970 running @ 4.25Ghz I've noticed performance changes with games that it use to run average.  Performance has gone down drastically with UT4.  More than 4 online players will cause the performance to decrease at a noticeable difference.  Maps that use to run well with 8-10 players are now more like the maps that would struggle.  The maps that struggled with 8-10 players well,,, now just struggle.  Pre 1809 update performance was acceptable 1903 for me takes away any competitiveness I had with games that ran average.