[1.7.10] Server Lag with perfectly fine TPS

I'm not sure if this is the right place to post this, but I didn't know where else I could find help with this, so if it's the wrong place I would appreciate it if you can link me up where I might find help with my problem, because frankly, I'm at wits end.

The problem:

My Server (modded, with Agrarian Skies 2, no deviation from the original modpack) shows constant console messages, that it can't keep up. For example:

[16:32:05] [server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 111430ms behind, skipping 2228 tick(s)

If I check ingame with /forge tps however, I get something like this:

/cofh tps returns similiar results, but the Lag is definitely there, because mining a block results in the block reappearing or dropping in your inventory after a 2-3 second delay. So I thought "Hm, maybe these are lagspikes and not continuous lag" and installed opis to take a closer look. To no avail - it gives me about the same TPS rate and with regard to tile entities etc. there doesn't seem to be anything particularly conspicuous (to me at least, maybe I'm missing something... well since I'm posting here I surely missed something). Only thing that seemed a bit off was, that opis displayed a server ping of 300-400 ms, but if I check ingame with Tab I got an all green connection. But still, I pinged the server manually, just in case, with this result:

--- PING hollohs.de (85.10.253.244) 56(84) bytes of data. ---
64 bytes from 85.10.253.244: icmp_seq=1 ttl=122 time=14.4 ms
64 bytes from 85.10.253.244: icmp_seq=2 ttl=122 time=14.2 ms
64 bytes from 85.10.253.244: icmp_seq=3 ttl=122 time=15.8 ms
64 bytes from 85.10.253.244: icmp_seq=4 ttl=122 time=16.3 ms

Nothing wrong there too it seems.

No excessive setups on the server so far, just a medium sized ME-System and about 100 machines all in all. Definitely nothing, that my server shouldn't be able to handle with ease.

So - does anyone have an idea what could be causing this lag? Any help would be greatly appreciated.

Cheers,

Tynian