@Leon, not directly related to com.atlassian.sal.api, but seeing that you’re still using <component-import> – aka. old-school “transformed” plugins and not using Spring-Scanner or similar techniques:
I urge you to take a look at the findings on Preparing for Confluence 9.0 - EAP coming soon - #43 by AndreasEbert
In short: I’m afraid the old-school way won’t work anymore → We/you have to switch to Spring-Scanner (or similar techniques).