Yes, of course it can move a few basis points, like a money market fund (compare https://www.vanguard.co.uk/professional/product/fund/money-market/9869/sterling

Yes, of course it can move a few basis points, like a money market fund (compare https://www.vanguard.co.uk/professional/product/fund/money-market/9869/sterling-short-term-money-market-fund-institutional-plus-gbp-acc https://www.vanguard.co.uk/professional/product/fund/money-m...). It shouldn't drop by 5% occasionally!