I keep on loosing internet connection after switching from optimum provided (leased) cable modem

Did you get the same model modem or something different. 

Anything near your modem like other electronic devices by chance. Where is the modem placed? 

If a new modem is now doing the same thing, seems like ISP needs to look at there logs and the condition of the modem signal when this is happending so they can see whats going on. You may need to get a modem from the ISP for short term use and see if it happens there. IF it does, then the ISP needs to figure this out.