Some of the plugins built on top of LTI mod and used custom instructor parameters are breaking in 2.8. The code which can be blamed lies in locallib.php in mod/lti. Function name is "lti_split_custom_parameters".
$lines = "explode("\n", $customstr); // Or should this split on "/[\n;]/"?

Earlier it was being split on /[\n;]/. So those plugins which were separating variables using semicolon are breaking now in 2.8. This line should be reverted back from explode to original preg_split.