Investigate misc eiger issues in June 2026

Now that the beamline has workarounds for serialising the eiger arming, disarming process, we should be able to better diagnose issues with them, a number of such issues have occurred in late June, we can investigate them more fully.

## Acceptance Criteria
- Specific criteria that will be used to judge if the issue is fixed

Start by reviewing the beamline workarounds for serialising the Eiger arming and disarming process, then examine the related issues from late June. The payload names no files, tests, or entry points, and the acceptance criteria are still a placeholder. Done should mean the affected issues are diagnosed and specific completion criteria are recorded.

Written by the indexing model from the issue text.