I have 3 viewers installed, the official one, the old Phoenix one and the latest Firestorm viewer.
Were you getting the following message when logging in using firestorm...
We are sorry, Linden Lab has discovered degraded performance on your connection to the region you are on. You will need to restart Second Life and log into a new region for the next 30 minutes to an hour. We apologize for the inconvenience.
For me I was getting this message for over 2 weeks everytime I logged in. I was just a cloud, tried everything like you said. Gave up after 2 weeks. I then tried again after 2 weeks then magically I could rezz my avatar again. I didn't need to change anything, it just suddenly started working again.
I'm so annoyed with the whole experience I decided to take time out because logging in is not a fun experience anymore. I'm not even sure if my avatar will rezz again and I do not want to spend my time looking around for empty sims to rezz my avatar, delete cache, gestures, detach/change hair base ect...
Another thing I noticed is if you had previously rezzed some items using an old viewer like Phoenix then try deleting them with a newer viewer like Firestorm it will not let you ( for me anyway ). I had to go back to the viewer I rezzed the items with to even see them and delete them with that particular viewer.
The problems are becoming so complicated. I have been in touch with the Phoenix/Firestorm people on their Jira and they are also confused about the "degraded peformance" message I put at the top of my message here, LL are not supplying any info as to what it means though so they are also confused without getting any answers from them.
Maxi