There are a couple points that could be causing this issue and without more info it's difficult.

• Incorrect static transform - a transform within your model may have the robot flipped along the X-Axis
• Incorrect odom to base_link transform - calculations to built up the tranform may have either simply bad math or flipped the robot over(or something).
• Incorrect odometry calcs - you don't describe the robot but if it is a differential drive then one motor is spinning forward and one backward and when calculating angle(rotation) maybe a minus sign got switched
• You're viewing the RVIZ robot from the under side in RVIZ so it only looks like it's turning the wrong way - verify that the "Invert Z axis" in RVIZ is not checked.
• You're viewing the real robot in a mirror and both the robot and RVIZ agree the TELOP is backwards.