Laravel TokenMismatch for one user only, possible reasons

Bugsnag has been reporting a single user keeps receiving a TokenMismatchException throughout the last few weeks on my production Laravel 5.1 environment, no other user has experienced this issue.

Stacktrace

Request Data (Obscured)

I considered perhaps the session was dying for this particular user, that they spent too long idle on the login page however I noticed sometimes they make 2 or 3 attempts in quick succession.

I'm preparing to contact the user but wish to understand the possibilities of why this exception keeps occurring other than a genuine attack before I do.

via Chebli Mohamed