Under 1.26, player OnStoreLoad from prior DayZ versions (e.g. 1.25) partially fails. This is due to two reasons:

1. PlayerAgentPool::STORAGE_VERSION was bumped to 137 under 1.26 Exp, but DayZ 1.25 had PlayerAgentPool::STORAGE_VERSION 100. Because PlayerBase::OnStoreLoad checks PlayerAgentPool::GetStorageVersion (which simply returns PlayerAgentPool::STORAGE_VERSION), loading the agent pool fails. This can be fixed by changing the line if (version < m_AgentPool.GetStorageVersion()) in PlayerBase::OnStoreLoad to if (version < 100) (changes should probably also be done for the other cases in OnStoreLoad where GetStorageVersion is used for ModifiersManager, SymptomManager, BleedingManagerServer and PlayerStomach).
2. PlayerStomach doesn't check the version when trying to read temperature in PlayerStomach::OnStoreLoad. Changing the line if (!ctx.Read(temperature)) to if (version >= 140 && !ctx.Read(temperature)) fixes that.