If a person who is handling cash and entering cash and bank transactions in ERP system, is maintaining bank reconciliation?

Yes I think it is control weakness and doesn't match with segregation of duties

Yes, the internal control is weak. Generally, there are four duties which have to be separated, i.e. custody over the assets, authorization, recording, and execution. In this scenario, the custodian and the book keeper is lodged to one person. It was weaken further when he is also in charged with the reconciliation. Hence he can do and conceal fraudulent transactions easily. 

It would depend on the clearance level of the initiation of the transaction , If the same person is doing everything then there is definitly a loophole . I would go by Mr. AAA Awads Answer in the context of propriety and Application of Workflow based on good accounting and auditing principles of Internal control. Better safe than to be sorry !!.

As ethics requires  us to follow the rule of segregation of duties... which is clearly not present so yes the controls are indeed weak.

YES : it is a control weakness

 For effective control

We must separate between the responsibilities or duties

noo