Hi, I am author of Photopea :) Photopea exists since September 2013, but Sketch support was added in April 2017.
I update the Sketch converter several times a week (when users report bugs / missing features). So now, if you load your Sketch file into PP, you may get a different PSD than you got a week ago.
Recently, I added the support for the Color Adjust of bitmaps, which is converted to Smart Adjust of Smart Objects. The file size limit will be fixed, too. Feel free to report any problems you have to https://github.com/photopea/photopea/issues . Half of problems is fixed within 30 minutes after reporting.
There were some “funny” bugs, e.g. Photoshop will not open a PSD, if it has more than 8000 layers, or if a name of some layer is longer than 256 characters. If such thing is in your Sketch file, Photopea will let you know / rename layers for you :)