I had a similar problem. Coffee, decaf, even dark chocolate would be very stimulating and would mess with my sleep, even a single cup in the morning. I tried quite a few things to solve this and ended up discovering that supplementing with molybdenum solved it. Molybdenum is an essential element important in the metabolization of some compounds, including caffeine. It's cheap and may be worth trying.
Also, I found that L-Theanine helped but only for maybe a week or so before it became less and less effective. For me, it was obviously a band-aid solution that wasn't correcting the underlying problem.
Also, I found that L-Theanine helped but only for maybe a week or so before it became less and less effective. For me, it was obviously a band-aid solution that wasn't correcting the underlying problem.