TL;DR: At some point, someone on the team will have work which can justifiably not go on the board. How is this handled in a sprint team when it is a long running thing?
Our team's technical leader has a number of things to be working on to support the team, which only that person can do (because of responsibility, contractual obligations, skill/knowledge level or system access permissions). Should that work go on the board?
The above is a fairly simple Yes, in my mind.
The problem is that the work in question may want to be kept away from the rest of the team because it might cause a distraction (it may result in their current work being disposed of at a later date but for valid reasons), it might simply be more interesting (another distraction they may waste time debating), or that including it in the daily scrum and other ceremonies exposes it to certain product owners who do/should not need to know about it.
Compounding the problem is that higher management accepts that there is certain work which technical leaders take on which is "off board" but still valuable. Much of this is exploratory/PoC type work and (regardless of where the budget comes from) is required but not team story related.
Further, that work is also (by it's exploratory nature) nearly impossible to estimate as it is often very "blue sky".
How should this work be handled?
Should the technical leader simply report that they deliver a lower amount of time to the team's sprints than regular team members or should we absolutely commit to having everything on the board, regardless? Or somewhere in between?