  Quasi-periodic oscillations (QPOs) have been widely observed in black hole
X-ray binaries (BHBs), which often exhibit significant X-ray variations.
Extensive research has explored the long-term evolution of the properties of
QPOs in BHBs. In contrast, such evolution in active galactic nuclei (AGNs) has
remained largely unexplored due to limited observational data. By using the 10
new XMM-Newton observations for the narrow-line Seyfert 1 galaxy RE J1034+396
from publicly available data, we analyze the characteristics of its X-ray QPOs
and examine their long-term evolution. The hard-band (1--4 keV) QPOs are found
in all 10 observations and the frequency of these QPOs evolves ranging at
$(2.47\text{--}2.83)\times10^{-4}\rm\ Hz$. Furthermore, QPO signals in the soft
(0.3--1 keV) and hard bands exhibit strong coherence, although, at times, the
variations in the soft band lead those in the hard band (the hard-lag mode),
while at other times, it is the reverse (the soft-lag mode). The observations
presented here serendipitously captured two ongoing lag reversals within about
two weeks, which are first seen in RE J1034+396 and also among all AGNs. A
transition in QPO frequency also takes place within a two-week timeframe, two
weeks prior to its corresponding lag reversal, indicating a possible coherence
between the transitions of QPO frequency and lag mode with delay. The diagram
of time lag versus QPO frequency clearly evidences this interconnected
evolution with hysteresis, which is, for the first time, observed among AGNs.
