Lost persistance in long term in redis without TTL
Preface: keys in Redis do not get deleted, unless explicitly requested or when the server is configured with an eviction policy (and RAM is pressured).

Regrettably, the most common cause for missing keys is security, or rather the lack of it. Script kids, leet haxors and regular bad guys take advantage of unprotected servers and cause all kinds of havoc. The first thing you need to do is ensure that the server is protected properly (i.e. is configured with a password and is not exposed to the world). For more details refer to https://redis.io/topics/security

After ruling out attacks and eviction policy configuration, the only remaining explanation is a rogue piece of code. From the server's side, you can try tracking this behavior using either the MONITOR command or by configuring keyspace events and subscribing to the relevant messages.