Matlab - Bode plot of Lag Filter + Integrator
I tried it in Octave, there's definitely a glitch like you said. I tried it with "Tustin" instead of "zoh", same result. 

However I was puzzled by your high sampling frequency. Your lag controller has a pole at s = -0.01 and a zero at s = -0.1, they are both "slow" while your sampling frequency is really high.

How to fix it : 
Change your sampling frequency to something much lower than 12 MHz, like 10 kHz for instance and replace "zoh" by "tustin". "Zoh" should only be used when converting a "process" transfer function to the discrete domain in order to take in account the effect of the DAC, we don't use it for compensators.

The root cause however is probably some quantization issue in the c2d function. 

FS = 10e3;
T_sample = 1/FS;

accu = tf([0 1], [1 0]);
lag = tf([10 1], [100 1]);

accu_d = c2d(accu, T_sample, "tustin");
lag_d = c2d(lag, T_sample, "tustin");

figure
bode(lag*accu, accu_d*lag_d);


Edit 1 :

The issue seems to be with the lag controller, not the accumulator. You should try to move the pole and the zero to the left, this should fix your problem since you must keep your sampling frequency really high:

try this (same DC gain, but pole and zero further to the left) : 

lag = tf([1 1000], [10 1000]);