Recently, my search console started showing an error regarding canonical tag as:
yourdomain.com/?SA
If I check the source code of my homepage, I see <a class='ab-item' aria-haspopup="true" href='/?SA&ai-debug-blocks=1&ai-debug-positions=0'> <a class='ab-item' href='/?SA&ai-debug-processing-fe=1'><span class="ab-icon">
?sa appears a total of 9 times in the homepage resource code.
i only see the ?sa query string on the Maichimp form and the Youtube subscribe button. If its not related to those, then check if you have any analytics or subscribe plugins that may be adding it