its not that the number is incorrect, its that it’s misnamed,
“invested” takes the cash spent on your open positions, it’s not tracking your deposited funds at all, so ISA limits don’t matter. as soon as you close and collect your losses or profits that number then drops to match your current open positions and once you open another position all the money you have just “invested” (spent) is added onto the total and it tracks the current share value against your purchase value.
it’s currently set so that its only ‘correct’ for people who add to their positions but NEVER close to realise the gains. it also means you see big spikes or dips in the graph that aren’t due to share price fluctuations, rather you adjusting your open positions.
there have been requests for it to be adjusted to track deposit’s instead of cash spent on shares for simplicity.