Android 8.0 Oreo seems to have an issue that can cause some apps to fail to inject custom actions, such as sharing, into the in-app context menu, according to a post made by Rory Harnisch on the Google+ page for Tasker plugins. Harnisch reported that the custom AutoShare context option was missing from his Tasker on Oreo, which prevents him from using any derivative functions thereof, let alone testing those functions in his own creations. Harnisch opened up an issue in Google's Issue Tracker for Android over the problem, in which he notes that the problem seems to stem from the Text Processing function introduced in Android 6.0 (Marshmallow). Harnisch also included a YouTube video demonstrating the issue, which has been included below. To round out his report, Harnisch provided a link showing that others are having similar issues. Thus far, five people have starred the issue, and a Googler has acknowledged the issue and picked up the assignment to take care of it.
The implications of this problem are fairly vast; not being able to inject custom context menu options, such as sharing options, can severely hinder the function of some apps. While there are many apps that can function relatively well without this ability, such as games, camera apps, keyboards, and the like, there are many other types of apps that will be affected heavily. The usefulness of photo editing and sharing apps, social media apps, and even niche apps like scanner apps that use your device's camera and multiple passes to scan and import documents could all have their functionality hampered by this bug.
The Text Processing code in question was originally introduced in Marshmallow to give developers a unified calling card that can be used to inject custom user-facing actions into context menus and other such places, where they would usually be forced to either adhere to Android's built-in standard action calls, or go to the trouble of writing customized ones from scratch into the app in question. This is accomplished via a flag that can make almost any text selectable and actionable. All developers had to do was, essentially, make a click or tap on a text action into a call for the system to select and act upon it in a manner that the developer defined elsewhere in the code. The failure here seems to boil down to the Text Processing code simply not recognizing AutoShare as an option in this instance, but with similar reports cropping up for different actions, the problem most likely goes deeper than that.