The text frame in the tolerance symbol (TOLERANCE) uses a different line weight than its text - it may appear thicker or thinner.
The tolerance framing uses the line properties (type, color, lineweight) given by the current dimension style settings, specifically it is tied to the dimension line settings. So please check these settings in the Dimension Style Manager - DIMSTYLE > Lines > Dimension lines.
Change the lineweight setting from "ByBlock" to "ByLayer" to apply any settings from the current layer as set in the Layer Manager. If you are using a plot style for printing, check also its line weight settings.
You can also preset this parameter with the system variable DIMLWD - change it to the value -1.