Edit: This question was based on a misunderstanding: I installed Chinese fonts in Ubuntu, where the default behaviour is to show Japanese characters. (I managed to fix this problem following the instructions here: https://askubuntu.com/q/901486; it was considered a bug.) Not realizing this was a software issue, I believed this problem related to 异体字 (yìtǐzì), or variant Chinese characters.
I've rephrased the question so the question is technically correct, related to the Chinese language, and so that the current answers actually answer the question.
No wonder I struggle to remember how to write 喝 (hē; to drink); this is what it looks like on my phone:
And this is what 喝 looks like on my computer:
This is the same character on the same website, but it's written in two different ways. It seems this is a common obstacle for people learning to write Chinese; see: Characters which have several different shapes.
These are variant Chinese characters 异体字 (yìtǐzì). I'm concerned about whether one is preferred over the other for the HSK. This would affect the reading and writing components.
Question: For the HSK, what do I need to know about characters which appear differently?