This is completely fine and normal and nothing to worry about.
To begin with the explanation, let me start by saying that a TieBreaker is just a special kind of diskless resource. The only difference in LINSTOR between a TieBreaker and a Diskless resource is how LINSTOR deals with this resource if for example you get an additional resource.
You usually only need a TieBreaker if you would otherwise only have 2 peers. If the connection between these two peers break, none of the two peers would know if the other one is still alive / could continue the service. This situation does not happen if you have 3 peers (regardless if they are diskful or diskless), since if you lose one connection, the majority (2) peers still see each other, can figure out that they have majority so they can keep quorum while the minority (the isolated peer) also knows that it no longer has quorum.
So, if you have 2 diskful + 1 TieBreaker resource in LINSTOR and you either delete 1 diskful or add another diskful, you will end up in either just 1 or 3 diskful peers. In neither case would a single additional TieBreaker help you. That is why LINSTOR would be “brave enough” to delete such a TieBreaker resource.
LINSTOR will under no circumstances delete a Diskless on its own, even if you would do the same as in the scenarios above. That means, if you go from 2 diskful + 1 diskless (not a tiebreaker this time) resources to 1 or 3 diskful, LINSTOR will not delete the diskless resource for you. Having 1 or 3 diskful + 1 diskless does not help you with quorum, but LINSTOR still thinks that you want this diskless resource to stay there (maybe a VM will try to access it soon).
Another (slightly briefer) approach to explain this: A TieBreaker is just a “LINSTOR-managed Diskless resource”. A TieBreaker is automatically created by LINSTOR and automatically deleted by LINSTOR if needed. The user can only create Diskless resources, no TieBreakers.
A side note: If a TieBreaker resource gets primary on DRBD level, it will automatically switch into Diskless state/type, since LINSTOR can no longer assume that the resource can safely be removed in case it is no longer needed as a tie-breaker.