Chat History Crashes

You can delete the chat log temporary while playing a campaign from the Settings tab. You can also delete it permanently from the Campaign Details page. If you want to make a backup before deleting it permenantly, you can view the chat log from the details page and save the resulting html file.

Every user, not just the GM, has access to the "Clear Current Chat Log" button when running a campaign. It's important to note that this button needs to be repressed if a user has to refresh their campaign's browser tab or exits and then rejoins the campaign. At this time, there's no export feature to save it out as plain text. Would be nice though. The dice images tend to be the biggest hog in the chat log. While it won't fix your current problem, because it's not a retroactive action, you can minimize the new chat log load by disabling advanced dice in the settings tab. Disabling chat avatars should help too.