The shared Elasticsearch cluster hosted in Toolforge was upgraded from 2.3.5 to 5.3.2 today (T164842). This upgrade comes with a lot of breaking API changes for clients and indexes, and should have been announced in advance. @bd808 apologizes for that oversight.
The stashbot, sal, and bash tools have been fixed to work with the new version. They all mostly needed client library upgrades and minor API usage changes due to the library changes. If you are one of the few other users of this cluster and your tool is broken due to the change and you need help fixing it, open a task or better yet come to the #wikimedia-cloud Freenode channel and ask @bd808 for help.