Yup it's normal. I've got about 1.2M right now.
There's no hard and fast rule but generally the longer tasks will build up more pending credit than the short ones. I usually build up the most when running GFN21/22.
Right now the best projects to run to keep pending credit to a minimum is the SOB & TRP double checks (and sieves).
Try not to focus too much on the pending, some tasks can take many months to clear and it will drive you nuts if you worry about it.