Controlling the contextual alternate in CSS when your font uses different characters for the same letters. It can be fun but sometimes it can also look a bit strange when 2 exacts consecutive letters look different. The good thing is we can usually have some control over this in CSS.
CSS font-feature-settings for font with OpenType features
For example, in a recent project we used this font Cy (an Adobe font) and this font has OpenType features such as Contextual Alternates that
This guide is great https://sparanoid.com/lab/opentype-features/
It tells us the to access Contextual Alternates we use calt
Then, to deactivate the Contextual Alternates I would add in my CSS the following.
font-feature-settings: "calt" 0;
Contextual Alternates in Sketch
To change this setting in Sketch, go to Text > OpenType Features > Contextual Alternates.
Hope this can help in your project and save you a bit of time.