If Projects have more than 200+ children (any record where top task = that project), Cost Plans opened from the Cost Plans related list (which is used OOB), the URL generated will not use the tinyurl parameter and instead, a list of all Cost Plans will be generated in the URL. Since browsers have a limited character limit for URLs, the page will be blank/broken (Varying browsers will have different URL browser string limitations)
Release or Environment
The Cost Plans OOB related list breaks and does not use the tinyurl parameter. (param_tiny).
Change this related list by swapping out for the 'Cost Plan->TopTask' related list (also OOB). The 'Cost Plan->Top task' related list performs the same list query as the previous.
1. Navigate to any Project/Project form
2. In the grey-header, select Configure > Related Lists
3. Replace 'Cost Plans' with the 'Cost Plan->Top task' related list
4. Click SAVE