Adding a temporal type (any) to SMAA component causes "edge detection" lines to be drawn to camera. Changing the temporal type causes these lines to become fainter each time until not visible. Entering playmode resolves the issues.

Repro Steps:

1) Open attached project and scene "Test"
2) Select "Main Camera" and add component "SMAA"
3) Change Temporal type to anything other than "None" and observe issue
4) Change Temporal type again and observe fainter lines
5) Enter playmode and observe issue is resolved