So sorry about your rejection buddy, completely sympathize with you. Based on the information from your GCMS notes and refusal letter one can conclude the following:
You worked in:
1) 2171 from 4 April 2014 - present; 1 year and 8 months (AOR 18 December 2015). The reference letter originally provided contained NO duties (since you received provincial nomination, the letter you provided to OINP must have listed the duties). You submitted a new reference letter with duties via CSE.
2) 2173 from 17 June 2014 - 8 April 2015; 9 months; as per GCMS, duties listed in the reference letter are consistent with NOC. The GCMS notes indicate that this experience meets the minimum requirements of 12 months of work experience, which is obviously a mistake since it only lasted 9 months. They corrected this in refusal letter stating you failed to demonstrate the required amount of experience.
Now, you have two experiences which completely overlap. I understand this, in reality, is the same job, but you decided to change the NOC because your job title altered after company acquisition. As you now already know, this was a mistake because job designations are completely irrelevant, only duties matter. Not to mention you inevitably created an utter confusion with supporting documents claiming two experiences at the same time.
Several questions arise from this. You obviously based your CEC eligibility on 2171 rather then 2173 since the latter would not qualify you (9 months only). Which NOC did you match your new (CSE) reference letter with? If you went with 2173, I would say this was not taken into consideration because you no longer met the program requirements (1 year in 2171). If you went with 2171, have you received an email any time after CSE stating that additional documents have been attached to your application?