I don't think it is a CPU- or GPU-based problem. I run a AMD Ryzen 7 2700X @3.7GHz with 32GB on memory, a AMD 850X, all installed on M2-SSD. It's not the newest, but i think…
Played today a little, building time lag is now "down" to 15s. Build about 10 tubes before... don't know what else changed. Building at an other, smaller base: no lags whatsoever.