I assume the host reloads when your character has no skills on joining (and presumably all attributes set to 5)? A stat boosting skill (such as Encourage in Man At Arms) may also get the game to reset the character properly.
Have you tried joining in a new game, or older save that you know worked before?
Have you tried joining from the online lobby (Join button in the main menu), using Direct Connection (using an IP address, or the Server ID that the host can get in the connectivity menu after loading a save [hit Esc to bring up a menu with that option, or click the diamond button on the top of the mini-map])?
Have you tried hosting? You can test with a new game, and if that works, each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin Enhanced Edition\PlayerProfiles\<ProfileName>\Savegames' folder, if your friend wants to zip the latest save and email it to you.
Has your friend double checked his in-game multiplayer options and firewall settings?
You can both try verifying local files: in the Steam library, right click on Divinity Original Sin Enhanced Edition and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Cache...' button.
If you check the Event Viewer, does that give an error code or 'Faulting Module' file name that might help identify the cause of the crash?
- click Start (or WinKey-R or WinKey-W in Win 8), then type "event viewer" into the search box
- after starting the Event Viewer, expand 'Windows Logs' in the left column and select 'Application'
- in the center column, look for a recent error (maybe sort by Date and Time) for the game
- check the information under the 'General' tab below the list of events, starting with "Faulting application name..."
Please email supportdos@larian.com, with a description of the problem (or link to this post) and the report.zip file (or a Dropbox or Google drive link, etc) generated by the
D:OS EE Analysis Tool (for Windows) for both of you.
Extract the zip file somewhere and run the AnalysisTool.exe. When that loads, browse to the install folder (if it is not automatically detected), optionally run the tests first, and then generate a report (it will be saved in the same location as the Analysis Tool).
The report will contain system and game information, as well as your saved games. To reduce the file size, you can delete all of the saves from the zip. Your frien can delete most of the saves, just leaving the latest save, and if older saves work fine, also leave the most recent you can join and oldest where your game crashes.
You can also either add a couple of the CrashDump files to the zip, or zip them separately.