Steps to reproduce:
1. Start a platform distro with the invoice example deployed
2. Start 4-5 process instances of the invoice process
3. Open All tasks filter (or filter for invoice definition) and check if all variables are visible for each task in the task list

Observed:
Some variables are not displayed in the task list (See screenshot)

Expected:
Each task shows the variables in the task list

Hint:
The current limit in the variable query is not sufficient. The query performed once for all tasks so we can have variables with the same name and different scope for each task and 5 * variableNames.size() is limiting too much.
https://github.com/camunda/camunda-bpm-platform/blob/917e154b4c84586860cd465772cd34d86f25e539/engine-rest/engine-rest/src/main/java/org/camunda/bpm/engine/rest/sub/runtime/impl/FilterResourceImpl.java#L541