Sitecore need to rebuild indexes from time to time to ensure system operations. Sitecore administrator need to do the same actions to rebuild custom indexes to update indexes after a content update.
sitecore_suggested_test_index is blocking all indexations taks. As you can see below, there a list of queued jobs, waiting for the end of indexation of sitecore_suggested_test_index.
After investigation, i found the following task responsible for this indexation.
Path : /sitecore/system/Tasks/Schedules/Content Testing/Rebuild Suggested Tests Index
It is running every 24 hours. Sometimes, there are many sitecore_suggested_test_index in the queue. It means, in our case, 24 hours is not enough to full rebuild the index. So, i have many tasks queued for sitecore_suggested_test_index plus others indexes blocked on the same time.
As we don’t use this index, we simply disabled the task.
Attention, if you use this index, the solution would be to reduce the frequency of you task running. You shouldn’t disable it.
The issue is known by Sitecore. Please find the KB on sitecore support site.