I attempted again with the following steps:
1. Moved all the files/folders in the blocks folder to a folder called old.bad
2. Moved all the files/folders in the chainstate folder to a folder called old.bad
3. Moved .lock, bootstrap.dat.old, and debug.log to a folder called old.bad
4. Downloaded a fresh copy of bootstrap.dat
5. Restarted v3.11.3.1-72cf1f3 with -reindex
Once again, the bootstrap.dat import failed after block 2,388,213:
2017-05-05 19:34:39 UpdateTip: new best=7494e20b179bf472436db5d9c4a921b6dcee823189b7fc90b0d8922658da357e height=2388213 algo=1 (scrypt) log2_work=73.838186 tx=2630332 date=2017-04-26 11:31:30 progress=0.949481 cache=43.8MiB(231560tx)
2017-05-05 19:34:39 LoadExternalBlockFile: Deserialize or I/O error - ReadCompactSize(): size too large
2017-05-05 19:34:40 Loaded 2395766 blocks from external file in 24061259ms