First; I ran into a bug where refining Tier 5 materials doesn't seem to count towards the activity card task. The first 5 counted, but the rest did not so the task sits at 5/50 and cannot be completed as far as I can tell.
The next bug I ran into was that you sometimes cannot change the skin on your gear. This is irritating considering you are awarded several skins in the season pass (and there are skins on the Twitch drop currently). It is also random which piece of gear will not let you change skin and then on your next login it changes which gear is bugged. For example; I could not change my chest piece skin this morning but all other slots were fine. Yesterday it was all gear slots I couldn't change.
While frustrating; these are not game breakers. I am still over all enjoying the season and finding myself doing more and more of the card activities. I tackled the first couple of quests in the storyline and hit level 39 now on the season!