Move from song to powerpoint lag
First, make sure you are on 18.104.22.168.
Second, try saving the PowerPoints as .PPT files instead of .PPTX. PPTX files take longer to open, especially on older and/or slower computers. PPTX are essentially a Compressed Archive file similar to a .Zip file with a PowerPoint inside. You are essentially decompressing (or opening) the archive to get to the actual PowerPoint file to be able to display it. .PPT files are the file without the Archive Wrapper so they are easier to open and display.
Next, without knowing your system specs it's difficult to determine if it's hardware or software related. If you have an older or less powerful computer and didn't have the issue with your prior system you may need to revert back to the previous release of EW, especially if it was a 7.1 version.
Also, make sure that your computer meets or exceeds the Recommended or Ultra requirements found in this support article. The Minimum specs are essentially garbage and mean absolutely nothing.