From my nginx access log:

your.ip.address - - [21/Feb/2024:06:50:09 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.sdf.org"
your.ip.address - - [21/Feb/2024:06:50:09 +0000] "POST /inbox HTTP/1.1" 400 0 "-" "Lemmy/0.19.3; +https://lemmy.sdf.org"
your.ip.address - - [21/Feb/2024:06:50:09 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.sdf.org"
your.ip.address - - [21/Feb/2024:06:50:09 +0000] "POST /inbox HTTP/1.1" 400 0 "-" "Lemmy/0.19.3; +https://lemmy.sdf.org"

2 of the entries are “https://lemmy.sdf.org/activities/like/88bc5b6d-f11f-4245-90aa-908e43befe97” being sent twice,
the other two are “https://lemmy.sdf.org/activities/like/437327e5-a262-46bc-8ce7-1c2c5bd440b3” being sent twice

I’ve reported this problem to other affected servers that I’ve seen:
the lemmy.ca post suggests the problem was something to do with running multiple containers with the same index number;
the endlesstalk.org post suggests that re-starting the backend containers is a fix
(their answers will likely more sense to you than to me, as I don’t run lemmy).

Thanks!