The spray can was still heavy so it was impossible that the low air pressure of an empty can could have been the cause of the erratic spray pattern.
Looking at the spray head I noticed that blobs of old paint had already formed at the tip of the spray nozzle. Although you can still see that there is a hole and since paint still comes out you'd have to assume that there is no blockage in the delivery system. I suspected that it was this glob of paint that was causing the erratic spray volume.
Initially I was thinking of dipping it in thinner but since the spray head looks like it is made of 100% plastic I was worried that I might deform it. So instead I took a file and filed off the paint from the tip of the nozzle. Luckily this assumption worked because the spray volume is now consistent and finely misted again.
Forgot to mention that I use commercial paints found in hardware stores to paint my model kits, but use the spray head of a GSI Creos Gundam Spray because I like the spray pattern. Hence the reason why it also clogs up due to frequent use.