Not queries. Just that one that has the problem.

That session has an open transaction. The column 'open tran count' shows 1, so open transaction, holding locks until commit/rollback. That's why it's blocking other sessions.

No, it won't be an engine bug.
Uncommitted transaction most likely. Exclusive locks are held until the transaction commits. Look at the open transactions, and make sure that you...

Max DOP = maximum number of concurrently *executing* threads for a single query. Not the maximum number of threads.
eg, for a query under maxdop 4, there will be a...

Plan guide for the query, if you want to use a hint. Otherwise, make sure there's useful indexes that can be used for that predicate.
You can't force an exec...

Performance tests aren't going to do much of anything to test for stability, and Windows not knowing about a write cache doesn't mean there's no write cache.

You need...

It doesn't. Anything in memory is lost on a restart.

Database recovery information comes from the transaction logs.

You'll need to set up an extended event session for that, it's not something tracked (you can get ratio of reads to changes per index from the index usage DMVs,...

This is a Microsoft SQL Server forum, you probably won't find Oracle query tuning people here.
Maybe try an Oracle-focused forum?

No. The data is ordered by the index key. Logically ordered, but still ordered.
The data doesn't have to be physically in key order on each page, and the...

Various, since I have a lot of clients. Lowest is probably 16GB, highest is 512GB.

My general comment is if your production server has less memory than my laptop...