From the Maplex help (Bold added for emphasis)
Using the Maplex Label Engine to rotate labels by an attribute value will turn each label on the map by a specified angle. The rotation angle is taken from an attribute value you've associated with the feature. You can also specify a rotation value to be added to this angle. The alignment type options allow you to orient your label to the angle in either a straight, horizontal, or perpendicular fashion. To prevent the labels from flipping upside-down when rotating around the feature, check the Keep label upright (may flip) check box.
If the center placement option is selected, the label is placed at the center of the symbol and rotated by the specified angle. If any of the offset placement options are selected, the label is placed at the offset distance and rotated to the specified angle. The selected placement position will be overridden, and the placement will be determined by the angle when you choose to rotate labels by an attribute value. The angle represents either geographic or arithmetic coordinates. Geographic rotates labels from north in a clockwise direction, while Arithmetic rotates labels from east in a counterclockwise direction.
Since you mentioned using offsets, per the help, my guess is some options are being overwritten.
by the way, you may want to move your question to https://community.esri.com/community/gis/mapping?sr=search&searchId=aa7e5039-338b-4cf6-bd0a-de867b42... or https://community.esri.com/community/mapping-and-charting?sr=search&searchId=8c375111-e0e1-4e3c-92ea... since " My Esri" is really more about license management, software diwnloads, etc. A moderator of this group can also move it ( timothy_hales-esristaff )
You can learn more about geonet communities and get hints about it https://community.esri.com/community/help-and-feedback?sr=search&searchId=10477da5-b3ec-4a99-8014-52...