"Select All" for ElementType::TEXT should select by subtype. And TextBase::subtype() should return substyle for MEASURE_NUMBER too.
In https://musescore.org/en/node/270358 a user unintentionally selected all text elements when right clicking a measure number and selecting all. This included the number text of every tuplet. This can cause a lot of problems because there is no other way to select the number text of tuplets, so if accidentally change things like the offest of the tuplet numbers, there is no easy way to revert the tuplets text positioning (other than modifying the .mscx by hand).
I investigated this in the subthread of https://musescore.org/en/node/270358#comment-824953 and solved it by having Select All Elements of Same Type functions Score::selectSimilar() and Score::selectSimilarInRange() include a cae for type == ElementType::TEXT, in which case select by subtype.
Also I noticed when selecting measure number, the inspector Substyle combobox was left empty. This was fixed by making sure to populate the substyle for MEASURE_NUMBERS in that combobox.
The problem happends in 2.1 and current 3.0 nightly.