I'm not sure how your credit system for tasks operates, but I'm having trouble receiving account credits for tasks completed. (It currently shows only 1333 credits on my tablet BOINC app...) I've had lots of problems receiving tasks and logging on to the app in the past.
Has anyone had a similar problem and could you give help please?

I just had a look, and you have just one host that is currently running just two tasks, neither of which have completed, let alone been validated. Until a task has been completed and validated by another host that completed the task with the same result, you wont get any credit for it. When a task has been completed and validated, then you get 667 Brownie points for it.

None of my hosts (which include an Android phone) are having difficulties receiving, completing, and returning tasks. I do have a number of tasks waiting for the second host to complete the task, and that wait can be lengthy if the task goes to one of those hosts that download a large number of of tasks, and then only complete one or two, if any, of them before disappearing off the internet.

A few users have reported difficulties uploading tasks, but that appears to be either a BOINC issue or a routing issue, not a Universe@Home issue. There is also a problem with some tasks either locking up or taking an extraordinarily long time to complete, but they are not very common.