I don't think you are a bad software engineer, most probably you are just not used to work in a big team. You are new in this middle size company and you are gi

I don't think you are a bad software engineer, most probably you are just not used to work in a big team. You are new in this middle size company and you are given the very badly written code which you are not familiar with at all. Most probably this code is big and exists for the long time and was modified chaotically to satisfy the urgent needs of customers. It is almost impossible to become efficient with this code immediately. May be I am wrong, but it seems you tried to work on your task without getting enough help from another people how know that code much better. The fact that your role is senior doesn't mean that you need to know everything and need to solve your problems alone. I work in a big company as a software developer and the interaction with people is the most important thing here.