I had similar issues with a Dappnode setup trying Nethermind as the EL client.

After a day or so of syncing it seemed to be consistently 32 blocks behind and would never catch up to 100%. Some digging suggested that it may be a lack of hardware resources because Nethermind is more hungry than Geth. There was a thread on Github suggesting it is not a resource issue and may be a bug in Nethermind. Ultimatley i did not find a definitive answer and moved on to trying Erigon instead. I would be suprised if it was a resource issue, i was using an I5 with 32GB RAM and 2Tb SSD, though the IOPS on the SSD are not the best spec possible it should be sufficient to sync.

Erigon seems to pose its own issue as Dappnode doesn't allow it as a full node repo at this time but it think it can still be configured as an EL client for staking, may just have to run a light client or a full Geth along side. However unsure if this will cause any unforeseen issues at this time.