user899: Earlier today I submitted a transaction on the Testnet. Shortly after I checked it using blockfrost and got the info my tx is included in block 3681998
A few hours later I checked again, but now the tx is included in block 3682001.
I am seeking for an explanation how that happened.
Thank you!

user4627: The latest blocks in the blockchain generally can change for a while until further blocks are created on top and push your transaction down the chain. The "deeper" it gets, the more likely it is not to change.
The two blocks you're pointing to are just ~3 minutes apart, so there doesn't seem to be anything abnormal about it. Here's a good read on these confirmation times / settlement windows.

user5926: My suspicion is as follows:

You saw the tx in block 3681998 (which must have been the chain tip).
Another block (competing with 3681998) was chosen by the consensus algorithm that did not contain that tx.
Block 3682001 was added that included that tx.


899: <p>Earlier today I submitted a transaction on the Testnet. Shortly after I checked it using blockfrost and got the info my tx is included in block <a href="https://testnet.cardanoscan.io/block/3681998" rel="nofollow noreferrer">3681998</a></p>
<p>A few hours later I checked again, but now the tx is included in block <a href="https://testnet.cardanoscan.io/block/3682001" rel="nofollow noreferrer">3682001</a>.</p>
<p>I am seeking for an explanation how that happened.</p>
<p>Thank you!</p>
 4627: <p>The latest blocks in the blockchain generally can change for a while until further blocks are created on top and push your transaction down the chain. The &quot;deeper&quot; it gets, the more likely it is not to change.</p>
<p>The two blocks you're pointing to are just ~3 minutes apart, so there doesn't seem to be anything abnormal about it. Here's a good read on these <a href="https://docs.cardano.org/core-concepts/chain-confirmation-versus-transaction-confirmation" rel="nofollow noreferrer">confirmation times / settlement windows</a>.</p>
 5926: <p>My suspicion is as follows:</p>
<ul>
<li>You saw the tx in block <code>3681998</code> (which must have been the chain tip).</li>
<li>Another block (competing with <code>3681998</code>) was chosen by the consensus algorithm that did not contain that tx.</li>
<li>Block <code>3682001</code> was added that included that tx.</li>
</ul>
