Like many devs, I use JSON.Serialize() with System.Debug() to output large lists/objects to the Debug Log when needed. Over the past few days, I've run into a new issue with Developer Console where double-clicking to open the full log message in a popup (to allow me to copy the output for pretty-printing elsewhere) no longer works as expected; the popup is truncating the debug message at arbitrary lengths between 310-340 characters. Same if I scroll the messages horizontally to view in-place; the output is truncated. If I download the log, the full contents of the JSON.Serialize() call are present in the log; this just appears to be a dev console issue.
The sandbox in question (CS52) is running Spring 19, but has been on this release since 9-Feb, and I'm certain this wasn't happening a couple of weeks ago. There's also nothing in the release notes that I could find regarding a change to the dev console. Also observed on CS13, and again, only in the past few days to a week.
Has anyone else experienced this? Is there a setting somewhere I can change? Needing to download every log is really going to slow down my pace of work.
Edit: just realized the "Open Raw Log" still lets me view and copy all of the text in the log, so at least I can avoid downloading. But it's still much less useful than the standard, filterable view.
Edit 2: Word of warning, leaving (large) raw logs open in my dev console window has led to problems with Chrome slowing down to the point that I've had to kill the worker process a few times today. I suggest closing them as soon as you get what you need.
Best Answer
Sounds like they added something to the Dev console to truncate long lines in spring 19 (On March 20, 2019 according to the Release Note changes).
Developer Console: String Values in Debug Logs Are Truncated
If you view the raw log you will still see the full log.
This also came up recently in system debug messages get trimmed. I suggested an alternative way to view the debug logs in that answer.