It is known that the first reading tends to be higher for a number of reasons with most of them being around the NIBP machine and cuff settling down after first placement, but other reasons include the same causes as “white coat syndrome“. People generally relax a bit after the first reading is taken.
For the reasons above the first reading is generally ignored.
Interesting you say you use an IBP app. Have you missed a leading “N” as IBP and NIBP use very different methods and will produce different result, with IBP being more accurate. IBP is not something you would do at home and it only used in a small number of areas in a hospital environment.