Elasticsearch request failed: 28 - Operation timed out after 1000 milliseconds with 0 bytes received

I have PHP web app which interacts with Elasticsearch. It worked well but recently i got error with next text:

2022-01-13 16:43:59 [95.161.173.18][4669][1tjhk618ubj7tjniq1utjpbntj][error][application] delete elastic
2022-01-13 16:44:00 [95.161.173.18][4669][1tjhk618ubj7tjniq1utjpbntj][error][application] Elasticsearch request failed: 28 - Operation timed out after 1000 milliseconds with 0 bytes received
2022-01-13 16:44:00 [95.161.173.18][4669][1tjhk618ubj7tjniq1utjpbntj][error][application] delete elastic
2022-01-13 16:44:02 [95.161.173.18][4669][1tjhk618ubj7tjniq1utjpbntj][error][application] Elasticsearch request failed: 28 - Operation timed out after 1001 milliseconds with 0 bytes received
2022-01-13 16:44:02 [95.161.173.18][4669][1tjhk618ubj7tjniq1utjpbntj][error][application] delete elastic
...

Meanwhile i see next in /var/log/Elasticsearch/elasticsearch_index_indexing_slowlog.log:

[2022-01-13T16:43:59,936][WARN ][index.indexing.slowlog.index] [5R0q8j_] [new_rid_elastic/0xTeeKV4T3myNSjWiL0oxQ] took[1.2ms], took_millis[1], type[rid-elastic], id[NXSuU34B855L8Ty5UGi_], routing[], source[{}]
[2022-01-13T16:44:01,542][WARN ][index.indexing.slowlog.index] [5R0q8j_] [new_rid_elastic/0xTeeKV4T3myNSjWiL0oxQ] took[2.2ms], took_millis[2], type[rid-elastic], id[540757], routing[], source[{}]
...

So what's going on? How to fix that time out related error and why it have occurred now?