I am one of the few who has had zero issues with my T300 in regards to GTSport. It's about 2-3 years old now (bought it when PS4 first came out) but to be fair, I haven't used it a lot, due to a lack of decent racing games. I have updated the wheel once, when PCars1 originally came out, because the FFB settings in that game were insanely overwhelming. Since then, I've changed nothing. I plugged into my PS4 last weekend, didn't change anything, and raced all weekend with zero issues, despite the horror stories I've read here on the forum.
Due to these horror stories, I will still avoid updating my wheel, until I've gotten more feedback from the community about the update and new firmware. The sad stories here on GTPlanet, do make me tempted to sell my wheel before I run into any issues, but I don't have a clue what I would upgrade to, without dropping a chunk of change on the new TG-T, which also has mixed reviews, and is made by the same company.
With the GTSport aspect out of the way, I will say this, for full disclosure.
When I originally bought my wheel, it had an incorrect outlet plug. Here in America, there's 1 'wide' prong, and one narrow prong on the wall plug, but mine had 2 wide prongs, so couldn't even be put into an American socket. I contacted the company, they requested a picture of the plug, and the serial number, and sent me a new one immediately, without needing me to send the original back.
In Project Cars, I had a similar issue that
@CJammer883 mentioned above. Midway through a race the FFB felt like it was 'fading', and would get extremely weak. I always assumed it was because it was overheating, that perhaps I had it turned up too high, or that I simply screwed up one of the million adjustments available in the PCars FFB menus. Haven't run into the problem in GTSport yet, so I'm not positive it's even a 'wheel' issue to be completely honest.
I do have some issues with the 'D Pad' from time to time sticking, or not 'staying' down. Trying to quickly scroll to the right amount of Fuel in the pits can be a pain. Lately a new problem has occurred, where the wheel randomly triggers the 'options' (pause/start) button, mid race. That's not so great, but it's once a day for the time being.
Anywho... hope to hear some good news about the updates in the coming days.