Linked Cells Not Updating

Within the same workspace I cells linked between sheets, just a simple integer that changes week on week depending on the new core data added. This workspace has been working great for about 2 months and all of a sudden a hand full of these linked cells don't update. E.g. Sheet 1 has a cell of value 175 and that is linked to a cell in sheet 2. This week Sheet 1 has updated to 195 but sheet 2 wont update this value unless it is unlinked, linked to a completely different cell first then relinked to the original correct cell.

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