. The problem turned out to be that there were more than 1000 transactions on my ZEC address with small amounts of 0.05 ZEC.
1000 transactions to sign is an extremely big data chunk that doesn't fit memory area allocated for relevant operations by BOLOS in Ledger. Thus splitting UTXOs in smaller groups containing, let's say up to 20 transactions each, and withdrawing these groups separately would be the wise approach to resolve your problem.