Reindex: 2 skipped annotations id 835827 and id 835834

[PeterCodar]

Yesterday, I have deleted all search indexes, replicated the data up-to-date and then executed:
sudo docker-compose exec indexer python -m sir reindex

The following 2 annotations id 835827 and id 835834 were skipped:

2020-09-05 14:28:51,024: Checking whether the versions of the Solr cores are supported
2020-09-05 14:28:51,090: Importing annotation...
2020-09-05 14:31:07,633: Skipping annotation with id 835827. The most likely cause of this is an unsupported control character in the data.
2020-09-05 14:31:07,639: Skipping annotation with id 835834. The most likely cause of this is an unsupported control character in the data.
2020-09-05 14:31:11,929: Successfully imported annotation!

Therefore the command
admin/check-search-indexes all
fails for the annotations:

CORE           STATUS  INDEX     DB
editor         OK      0         /0
instrument     OK      994       /994
series         OK      11999     /11999
place          OK      43144     /43144
event          OK      44424     /44424
tag            OK      100668    /100668
area           OK      118283    /118283
label          OK      185708    /185708
cdstub         OK      293239    /293239
annotation     --      374482    /374484
work           OK      1364636   /1364636
artist         OK      1697014   /1697014
release-group  OK      2066573   /2066573
release        OK      2617510   /2617510
url            OK      6976326   /6976326
recording      OK      23085150  /23085150

[PeterCodar]

Two more...

2020-10-01 13:23:20,648: Skipping annotation with id 848977. The most likely cause of this is an unsupported control character in the data.
2020-10-01 13:23:21,574: Skipping annotation with id 849005. The most likely cause of this is an unsupported control character in the data.

[michaelchisari]

I'm seeing 5 annotations skipped on a fresh install

2020-11-21 06:26:10,296: Skipping annotation with id 835834. The most likely cause of this is an unsupported control character in the data.
2020-11-21 06:26:13,987: Skipping annotation with id 835827. The most likely cause of this is an unsupported control character in the data.
2020-11-21 06:26:18,981: Skipping annotation with id 848977. The most likely cause of this is an unsupported control character in the data.
2020-11-21 06:26:23,460: Skipping annotation with id 849005. The most likely cause of this is an unsupported control character in the data.
2020-11-21 06:26:28,722: Skipping annotation with id 851348. The most likely cause of this is an unsupported control character in the data.