When we have a store with promotional price tables created and large shopping carts applying the promotions, it causes slows in the performance of the purchase and leads to timeout errors in the cart.

Any actions on the cart can trigger errors, such as adding items, editions, input zip code, etc will compromise the performance of the purchase.

We cannot know for precise which number of promotional price tables being calculated in the cart or the quantity of items added in the cart will start triggering the timeout errors or slowing down the performance, from what was analyzed it can happen with any significant amount.

Create multiple promotional price tables and a shopping cart with many items (here we cannot point a clear number, such as 50 or 100, it depends on the promotions)

Unfortunately, we do not have any workarounds for this, deactivating the promotions and using the price module to insert the prices would help.