After login to cumulocity page, getting error as “page unresponsive” and taking more time to navigate through pages. Here I am attaching a screenshot as well.
That’s quite a lot of measurements in one graph 
The Measurements tab in Device Management tries to visualize all of them unfiltered which is in your case too much data to handle and not readable at all.
Workaround: Use the Cockpit + Dashboard and select all the data points which are relevant for you only (not all of them).